[etiennemunnich]

Summary

Add slash-delimited regex support for the variable-key part of
ctl:ruleRemoveTargetById and ctl:ruleRemoveTargetByTag.

Patterns are compiled once at config load (not per request). Literal
targets keep working. Empty or unclosed /…/ fail at config load.

Slash-aware lexer: commas inside /…/ are part of the pattern (so
{m,n} works); commas outside still separate chained actions
(…,deny). Slash-bearing literal keys (e.g. ARGS:a/b) no longer
swallow following actions. Regex ctl exclusions do not drop variables
declared via VariableRegex (synthetic COLLECTION:regex(…) names).

ModSecurity JSON argument names use json.array_N.* (not Coraza’s
json.N.*):

ctl:ruleRemoveTargetById=932125;ARGS:/^json[.]array_[0-9]+[.]JobDescription$/
ctl:ruleRemoveTargetByTag=XSS;ARGS:/^json[.]array_[0-9]+[.]JobDescription$/

Fixes #3505

Problem

JSON body processing generates argument names with unpredictable numeric indices (json.0.JobDescription, json.1.JobDescription, ...). Without regex key support, operators must either:

1. Write one exclusion per possible array index (impractical)
2. Exclude the entire ARGS collection from the rule (too broad, loses protection)
3. Use path-based exclusion (loses all CRS protection for the endpoint)

This is a common pain point for anyone running CRS with JSON/GraphQL APIs.

Approach

Following your guidance in the issue discussion, the regex is compiled once at config load — never recompiled per request. This directly addresses the concern about the v2 PR #3121 where regex compilation ran on every exclusion check.

How it works

1. Detection: In init(), the /pattern/ delimiter is detected in the target string (e.g. ARGS:/^json\.\d+\.Field$/)
2. Compilation: The pattern is compiled via Utils::Regex (PCRE2 by default, PCRE1 with --with-pcre) at config load time
3. Storage: Compiled regex is stored as shared_ptr<Utils::Regex> — shared across all requests, zero per-request allocation
4. Matching: During rule evaluation, searchAll() runs against the short variable-key string (typically 10-40 chars)
5. Backward compat: Literal targets (ARGS:password) continue to work unchanged via the existing == / case-insensitive comparison

Shared design for ById and ByTag

Both actions use a common RuleRemoveTargetSpec struct with matchesFullName() and matchesKeyWithCollection() methods, avoiding code duplication.

Lexer change

The scanner character class REMOVE_RULE_TARGET_VALUE (previously REMOVE_RULE_TARGET_BY_ID_VALUE, used only by ById) is now shared by both ById and ByTag. It includes regex metacharacters (^ $ + ( ) | ? \) but not comma — so chained ctl: actions still split correctly on ,.

Context: ModSecurity v2 and Coraza

Engine	ById	ByTag	ByMsg	Regex keys
ModSec v2 (v2.9.12)	✅	✅	✅	❌
ModSec v3 (upstream)	✅	✅	❌	❌
Coraza (post PR #1561)	✅	✅	✅	✅
This PR	✅	✅	—	✅ (ById + ByTag)

This PR adds regex key support to the two actions that v3 already has (ById, ByTag). The missing ctl:ruleRemoveTargetByMsg is a separate, larger discussion and is intentionally excluded.

Files Changed (11 files)

File	Change
headers/modsecurity/rule_remove_target_entry.h	New. RuleRemoveTargetSpec, ByIdEntry, ByTagEntry structs
headers/modsecurity/transaction.h	ById + ByTag list types updated to use new entry structs
src/actions/ctl/rule_remove_target_by_id.cc	Parse /pattern/, compile regex in init()
src/actions/ctl/rule_remove_target_by_id.h	Add shared_ptr<Regex> member
src/actions/ctl/rule_remove_target_by_tag.cc	Parse /pattern/, compile regex in init()
src/actions/ctl/rule_remove_target_by_tag.h	Add shared_ptr<Regex> member
src/parser/seclang-scanner.ll	REMOVE_RULE_TARGET_VALUE shared by ById + ByTag
src/rule_with_operator.cc	Both match paths use target.matchesFullName() / matchesKeyWithCollection()
test/test-cases/regression/issue-3505.json	5 tests: ById regex, ByTag regex, ByTag literal compat
test/test-cases/regression/issue-3505-crs-ctl-byid-tag-msg.json	2 CRS-style tests with @detectSQLi + JSON body
test/test-suite.in	Register new test files

Test Results

7 new tests, all passing:

Test	Description
ById regex — JSON array keys	ARGS:/^json\.\d+\.JobDescription$/ excludes dynamic JSON args
ById regex — suffix match	ARGS:/mixpanel$/ excludes args by suffix pattern
ByTag regex — JSON array keys	Same as above, matching rules by tag
ByTag regex — suffix match	Same as above, matching rules by tag
ByTag literal — backward compat	ARGS:password — proves literal targets still work unchanged
CRS-style ById + @detectSQLi	Realistic JSON POST with SQL injection, excluded by regex key
CRS-style ByTag + @detectSQLi	Same scenario, excluded by tag + regex key

Full regression suite: 5005 total, 4987 pass, 18 skip, 0 fail, 0 error.

Performance

Benchmark: 25,000 iterations × 5 trials, JSON POST with 20 ARGS keys, 3 detection rules (@detectSQLi, @detectXSS, @rx), 2 regex exclusions (one ById, one ByTag).

Scenario	Median	Per-request
Baseline (no exclusions)	1,209 ms	0.048 ms
With regex exclusions	1,326 ms	0.053 ms
Overhead	+117 ms	+0.005 ms/req (+9.7%)

Scaling with more ARGS keys:

Keys/request	Baseline	With regex	Overhead
20	1,209 ms	1,326 ms	+9.7%
50	2,620 ms	2,873 ms	+9.7%
100	5,199 ms	5,543 ms	+6.6%

The overhead scales linearly with ARGS count — no exponential blowup. At 100 keys (an extreme JSON body), the per-request cost is +0.014 ms. The cost is the searchAll() call on short variable-name strings against precompiled PCRE2 patterns.

Key design decisions keeping performance in check:

• Regex compiled once at config load, stored as shared_ptr
• searchAll() runs on short strings (variable names, typically 10-40 chars)
• Literal targets use existing == comparison — no regression for non-regex users

Summary by CodeRabbit

New Features

• Target exclusions by rule ID or tag now support slash-delimited regular expressions, including collection-scoped patterns.
• Commas inside regex patterns remain part of the pattern, while commas outside continue to separate chained actions.

Bug Fixes

• Regex exclusions now match variable keys and collection-qualified variables more precisely, without affecting unrelated variables.
• Invalid, empty, or unclosed regex patterns are rejected.
• Slash-bearing literal targets no longer consume following actions.

Tests

• Added regression coverage for regex and literal exclusions, chained actions, JSON targets, and invalid patterns.

[etiennemunnich]

Known limitation: {m,n} quantifiers in regex keys

After reviewing the discussion in PR #3121 between @airween, @marcstern, and @dune73, I want to flag one inherent limitation.

The comma inside {m,n} quantifiers breaks parsing. For example:

# This will NOT work — comma inside {2,5} terminates the token:
ctl:ruleRemoveTargetById=1;ARGS:/^field\d{2,5}$/

# Parser sees: ARGS:/^field\d{2   ← token ends at comma

This is the same constraint discussed at length in PR #3121 — the comma is the SecLang action separator, and it cannot be included in the lexer character class without breaking ctl:a=...,ctl:b=... chaining.

Workarounds are straightforward:

Instead of	Use
\d{2,5}	\d\d+ or \d+
[a-z]{3}	[a-z][a-z][a-z] or [a-z]+
.{1,10}	.+

The character class does include { and } (updated in latest push), so fixed-count quantifiers like \d{3} work fine — only the comma-containing {m,n} form is affected. This matches the same trade-off the v2 PR makes.

I believe this is acceptable for the target use case (JSON key patterns like ^json\.\d+\.FieldName$ and cookie name patterns like ^sess_[a-f0-9]+$), which don't need {m,n}.

[airween]

Hi @etiennemunnich,

thanks for this great PR! Really excellent work, congrats!

There are some reports from SonarCloud, please take a look at them, but I think that would be enough to check only headers/modsecurity/rule_remove_target_entry.h (these 3 issues).

Regarding to your knowing {m, n} limitation: I see that pain, probably we should check the parser, maybe we can figure out something to resolve this.

[Copilot]

Pull request overview

Adds regex support for the variable-key portion of ctl:ruleRemoveTargetById and ctl:ruleRemoveTargetByTag, enabling scoped exclusions for dynamic JSON keys (e.g., json.0.Field, json.1.Field) without disabling entire collections.

Changes:

• Introduces RuleRemoveTargetSpec / entry structs and updates transaction storage for rule-remove-target state.
• Parses /pattern/ targets at config load time and stores a compiled regex for ById/ByTag.
• Updates rule evaluation paths and adds regression + CRS-style tests for the new behavior.

Reviewed changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
tools/rules-check/Makefile.am	Adds include path to accommodate new header dependencies.
test/test-suite.in	Registers new regression test files.
test/test-cases/regression/issue-3505.json	Adds regression tests covering ById/ByTag regex and literal compatibility.
test/test-cases/regression/issue-3505-crs-ctl-byid-tag-msg.json	Adds CRS-style JSON tests validating regex exclusions with SQLi detection.
test/benchmark/Makefile.am	Adds include path to accommodate new header dependencies.
src/rule_with_operator.cc	Switches exclusion checks to new matches*() helpers for ById/ByTag.
src/parser/seclang-scanner.ll	Broadens lexer token class for remove-target values to allow regex metacharacters.
src/actions/ctl/rule_remove_target_by_tag.h	Stores a precompiled regex pointer for ByTag action.
src/actions/ctl/rule_remove_target_by_tag.cc	Detects /pattern/, compiles regex in init(), stores structured entry in transaction.
src/actions/ctl/rule_remove_target_by_id.h	Stores a precompiled regex pointer for ById action.
src/actions/ctl/rule_remove_target_by_id.cc	Detects /pattern/, compiles regex in init(), stores structured entry in transaction.
headers/modsecurity/transaction.h	Updates transaction fields to new entry types and includes new header.
headers/modsecurity/rule_remove_target_entry.h	New public header defining target spec + ById/ByTag entry structs and match helpers.

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[airween]

@etiennemunnich,

also, unfortunately all Windows tests were failed, for eg this one.

Honestly, I can't see the root cause after a quick look, namely why the compiler does not find the pcre2.h...

Meantime Copilot also made a review, please take a look at them too. Maybe this explains the Windows build error.

[Copilot]

Pull request overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated 6 comments.

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[airween]

@etiennemunnich,

there are some new Copilot notes, please take a look at them.

[sonarqubecloud]

Quality Gate passed

Issues
9 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
1.1% Duplication on New Code

See analysis details on SonarQube Cloud

[coderabbitai]

No actionable comments were generated in the recent review.

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• test/test-cases/regression/issue-3505.json

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Walkthrough

The ctl:ruleRemoveTargetById and ctl:ruleRemoveTargetByTag actions now accept slash-delimited regex targets. The parser preserves commas inside regexes, the actions compile and store valid patterns, and rule evaluation uses target matchers for variables and keys.

Changes: Regex target removal

Layer / File(s)	Summary
Parse and store regex targets headers/modsecurity/rule_remove_target_entry.h, headers/modsecurity/transaction.h, src/parser/seclang-scanner.ll, src/actions/ctl/rule_remove_target_by_id.*, src/actions/ctl/rule_remove_target_by_tag.*, src/Makefile.am	The scanner recognizes slash-delimited regex targets, including commas inside patterns. The ById and ByTag actions reject empty, unclosed, or invalid regexes and store structured target entries in transaction state.
Match targets during rule evaluation src/rule_remove_target_entry.cc, src/rule_with_operator.cc	Target matcher methods support literal and regex matching against variable names and keys. Matching checks collection prefixes and skips synthetic regex(...) full names.
Validate target parsing and matching test/test-cases/regression/issue-3505*.json, test/test-suite.in, CHANGES	Regression cases cover regex and literal exclusions, collection scoping, slash-aware parsing, parser errors, chained actions, and ById and ByTag behavior. The test suite includes the new cases, and the changelog records the changes.

Priority: Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Scanner as SecLang scanner
  participant Action as ById or ByTag action
  participant Regex as Utils::Regex
  participant Transaction
  participant Evaluator as RuleWithOperator
  Scanner->>Action: Parse target value
  Action->>Regex: Compile slash-delimited pattern
  Action->>Transaction: Store target entry
  Evaluator->>Transaction: Read target entries
  Evaluator->>Regex: Match variable name or key

Loading

Merge Risk: Moderate · up to 93b3d

Regex exclusions can process long request keys without the specified safeguards, and ByTag literal exclusions can now remove differently cased rule variables. Address or explicitly accept these risks before merging.

Pre-merge checks: 3 · 2

Failed checks: 2 warnings

Check name	Status	Explanation	Resolution
Linked Issues check		Issue [#3505] requires regex matching for ctl:ruleRemoveTargetById, unchanged literal support, and configuration-load rejection of invalid regexes. The current code compiles regexes in `RuleRemoveTa…	Implement the ReDoS controls required by issue #3505. Limit evaluated variable names to 256 characters, apply a PCRE match limit to this matching path, and reject known risky patterns during configuration loading. Add regression tests for t…
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 8 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: adding regex key support to both target-removal actions.
Out of Scope Changes check		The ByTag implementation extends the same regex variable-key exclusion through shared parsing, storage, matching, and regression tests. The lexer changes support the requested target syntax and chaine…
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.

Full details: Out of Scope Changes check

Explanation

The ByTag implementation extends the same regex variable-key exclusion through shared parsing, storage, matching, and regression tests. The lexer changes support the requested target syntax and chained actions. The added changelog and tests document or verify the feature. The pull request does not implement the separately excluded ctl:ruleRemoveTargetByMsg behavior, and no unrelated change is demonstrated.

Full details: Linked Issues check

Explanation

Issue [#3505] requires regex matching for ctl:ruleRemoveTargetById, unchanged literal support, and configuration-load rejection of invalid regexes. The current code compiles regexes in RuleRemoveTargetById::init() and matches variable keys. The current code does not implement the issue's required ReDoS controls. RuleRemoveTargetSpec::matchesKeyWithCollection() and matchesFullName() call regex->search() without a 256-character subject limit or a path-specific PCRE match limit. RuleRemoveTargetById::init() also does not reject known risky patterns at configuration load.

Resolution

Implement the ReDoS controls required by issue #3505. Limit evaluated variable names to 256 characters, apply a PCRE match limit to this matching path, and reject known risky patterns during configuration loading. Add regression tests for these controls.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 8 files. (1 skipped: 1 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

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[etiennemunnich]

Hi there, returning to this. rebased PR onto current v3/master.

Addressed the following:

• Merge conflicts with upstream lexer work (fix(lexer): rejection of '@' in ctl:ruleRemoveTarget actions (#3565) #3589) resolved
• Slash-aware parsing for COLLECTION:/regex/: commas inside /…/ are part of the pattern (so {m,n} works); commas outside still split chained actions (…,deny)
• Fail-closed for empty/unclosed regex; did not adopt the broader Copilot class that still bans commas (that wouldn’t fix {m,n})
• Testing coverage expanded: {m,n} ById/ByTag, cookies, headers, JSON json.array_N, chained ,deny
  Local make check green; scoped cppcheck + Semgrep clean on the tip

Happy to adjust if you’d rather a different lexer approach.

[coderabbitai]

Actionable comments posted: 2

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Inline comments:
Review comments at @src/rule_remove_target_entry.cc:
- Line 61: Update the matching logic in both actions that evaluate
request-controlled keys to reject keys longer than 256 characters and use the
match-limit-aware Regex::search overload with match context. In both actions’
init() methods, reject known unsafe patterns; preserve existing behavior for
safe, in-limit keys.

Review comments at @src/rule_with_operator.cc:
- Line 179: Update the ByTag full-name matching around m.target.matchesFullName
and variable->m_fullName to use exact string equality for literal targets while
preserving regex matching for regex targets; do not change ById matching
behavior.

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• CHANGES
• headers/modsecurity/rule_remove_target_entry.h
• headers/modsecurity/transaction.h
• src/Makefile.am
• src/actions/ctl/rule_remove_target_by_id.cc
• src/actions/ctl/rule_remove_target_by_id.h
• src/actions/ctl/rule_remove_target_by_tag.cc
• src/actions/ctl/rule_remove_target_by_tag.h
• src/parser/seclang-scanner.cc
• src/parser/seclang-scanner.ll
• src/rule_remove_target_entry.cc
• src/rule_with_operator.cc
• test/test-cases/regression/issue-3505-crs-ctl-byid-tag-msg.json
• test/test-cases/regression/issue-3505-crs-matrix.json
• test/test-cases/regression/issue-3505-slash-aware.json
• test/test-cases/regression/issue-3505.json
• test/test-suite.in

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[etiennemunnich]

looked at both actionables.

On rule_remove_target_entry.cc: compile-once was the #3505 bar and the tip does that; empty/invalid already fail closed. Skipping the vague unsafe-pattern reject. Length cap / SecPcreMatchLimit can be follow-ups (tunable + searchOneMatch wiring), not merge blockers. Coraza didn’t ship those three either.

On ByTag case: pre-change ByTag was exact ==, ById was already CI; sharing matchesFullName made ByTag CI too. Leaving that unify — restoring ByTag-only exact match would re-split ById/ByTag for old byte-compat, and Coraza matches these exception keys case-insensitively so we would not be introducing any inconsistent approaches when folk are managing rules.

[coderabbitai]

Actionable comments posted: 1

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Inline comments:
Review comments at @src/parser/seclang-scanner.ll:
- Line 493: Update REMOVE_RULE_TARGET_VALUE to require the target atom followed
by :/ before matching a closed regex, so slash-bearing literals remain handled
by REMOVE_RULE_TARGET_LIT. Add a regression test for a slash-bearing literal
followed by a later slash, such as the provided rule input, and verify the
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• CHANGES
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• src/rule_remove_target_entry.cc
• test/test-cases/regression/issue-3505-claude-1-3.json
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• CHANGES

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[sonarqubecloud]

Quality Gate passed

Issues
14 New issues
4 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
1.0% Duplication on New Code

See analysis details on SonarQube Cloud

[fzipi]

Thanks @etiennemunnich, this is a solid piece of work, and the test coverage is very thorough. I built 93b3dc29 locally (macOS, PCRE2). The full suite is green (5188 total, 5168 pass, 20 skip, 0 fail), and so are all 57 cases in the five new files. The matching side looks right to me: the regex is compiled once in init(), the collection prefix is checked before the key regex, scalar variables are rejected, and VariableRegex names are skipped.

I found one blocking problem in the lexer.

1. A / inside the pattern can still swallow the actions that follow (blocking)

The PR documents escaped \/ as supported (T8/T8b), but it breaks as soon as a later action in the same rule also contains a /:

# Loads fine, but deny/status are swallowed into the regex: the rule no longer blocks
SecRule ARGS:x "@contains a" "id:1,phase:2,ctl:ruleRemoveTargetById=2;ARGS:/^a\/b$/,deny,status:403,setvar:tx.dir=/"

# Fails at load with "Unclosed regex ...: ARGS:/^a\/b$/,deny,status:403,tag:'a/b'"
SecRule ARGS:x "@contains a" "id:1,phase:2,ctl:ruleRemoveTargetById=2;ARGS:/^a\/b$/,deny,status:403,tag:'a/b'"

With the first rule, ?x=a returns 200 instead of 403. An unescaped slash (ARGS:/^a/b$/,deny,...,setvar:tx.dir=/) behaves the same way. In each case the second slash of the pattern is taken as the end of the regex, and then:

• REMOVE_RULE_TARGET_RECHAR contains \\, so a backslash can be consumed as an ordinary character and the following / closes the span. The escape alternative \\. is never forced.
• REMOVE_RULE_TARGET_VALUE repeats the /…/ group with (…)+, and the body allows ,. After a slash in the pattern, flex's longest match keeps opening new /…/ groups through ,deny,… up to the next slash anywhere later in the action list.

The silent case needs the swallowed text to end in /, so it is unlikely in practice. Still, losing a disruptive action without any error is the exact failure this lexer change is meant to prevent. Two small changes fix both cases for me:

-REMOVE_RULE_TARGET_RECHAR               [a-zA-Z0-9_\-\.\*\:\;\$@\=\(\)\[\]\'\^\+|?\\{},]
+REMOVE_RULE_TARGET_RECHAR               [a-zA-Z0-9_\-\.\*\:\;\$@\=\(\)\[\]\'\^\+|?{},]
 REMOVE_RULE_TARGET_REBODY               (\\.|{REMOVE_RULE_TARGET_RECHAR})*
-REMOVE_RULE_TARGET_VALUE                {REMOVE_RULE_TARGET_LIT}+[:]([/]{REMOVE_RULE_TARGET_REBODY}[/]{REMOVE_RULE_TARGET_NAME}*)+
+REMOVE_RULE_TARGET_VALUE                {REMOVE_RULE_TARGET_LIT}+[:][/]{REMOVE_RULE_TARGET_REBODY}[/]{REMOVE_RULE_TARGET_NAME}*

With these changes, both rules above block as expected, ARGS:/^a\/b$/ still works, and a bare ARGS:/^a/b$/ still loads through the literal rule (init() compiles ^a/b$). All 57 new cases and the full suite still pass. Please add the two rules above as regression cases.

2. Unsupported regex characters give a misleading error (non-blocking)

!, <, >, #, %, &, ~ and whitespace are not in the body class. So ARGS:/^(?!keep)json/ fails with Unclosed regex in ctl:ruleRemoveTargetById: ARGS:/^(?, and so do named groups and lookbehinds. Failing at load time is fine, but the message sends people looking for a missing /. I suggest something like "unclosed regex or unsupported character", plus a note in the docs about which characters are allowed and that / must be escaped as \/.

3. Public API change (non-blocking, for the release notes)

Transaction::m_ruleRemoveTargetById and m_ruleRemoveTargetByTag are public members, and their element types change. The layout doesn't move (std::list has the same size whatever it holds), but any code that reads those members won't compile any more. Also, ByTag literal matching in getFinalVars is now case-insensitive, as ById already was. That's fine and you've explained why, but the CHANGES entry should mention both points.

4. Housekeeping (nits)

• CHANGES: the four entries describe one feature as it evolved across the PR's commits. Please merge them into one entry in the usual [feat: …] [PR #3526 - @etiennemunnich] style.
• test/test-cases/regression/issue-3505-claude-1-3.json: please rename it (e.g. issue-3505-lexer.json). Five files for one feature is also a lot; two or three would be easier to maintain.
• test/test-suite.in: the new lines sit between config-update-target-by-id and config-update-target-by-msg. Please move them to their alphabetical place.
• The ~30-line regex detection in init() is copied verbatim between rule_remove_target_by_id.cc and rule_remove_target_by_tag.cc. A helper next to RuleRemoveTargetSpec (taking the action name for the error message) would keep them from drifting.
• src/actions/ctl/rule_remove_target_by_{id,tag}.h include src/utils/regex.h only for a shared_ptr member. The forward declaration in rule_remove_target_entry.h is enough, so the include can move to the .cc files.

On the open question to @airween about a key-length guard or match limit: I don't think it should block this PR. The pattern is admin-supplied, and Regex::search() is the same unlimited call that VariableRegex and KeyExclusionRegex already use for ARGS:/…/ targets. If we want SecPcreMatchLimit honoured there, it should be done for all three in one follow-up.

Requesting changes for item 1 only. The rest can be handled in this PR or a follow-up.