CVE
OWASP CRS: ReDoS in shared unix-shell-evasion regex-assembly include (12 RCE rules) - PCRE2 backtracking-limit exhaustion causes detection…
CRS deployments on ModSecurity v2 or v3 that load the unix-shell-evasion RCE rules are exposed. Fixed in CRS 4.28.0; the vendor rating is not given.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 3.3.10, 4.25.1, 4.28.0
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 3.3.10, 4.25.1, 4.28.0.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 26/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
The OWASP Core Rule Set (coreruleset) has a regular-expression denial-of-service flaw in a shared regex-assembly include used by 12 Unix remote code execution detection rules. A remote attacker can send a single crafted request without logging in, which can bypass detection and exhaust CPU.
Read the original description
The OWASP core rule set (CRS) is a set of generic attack detection rules for use with compatible web application firewalls. Prior to versions 3.3.10, 4.25.1, and 4.28.0, regular-expression denial of service (ReDoS) affects a shared regex-assembly include used to build 12 Unix RCE detection rules in CRS v4, and the same ambiguous pattern was present in the manually-assembled regexes in 4 rules in CRS v3.3. With a single, unauthenticated, crafted request, the generated pattern drives PCRE2 past its backtracking limit. When PCRE2 exceeds that limit, the @rx operator returns an error rather than a match result, which results in detection bypass and CPU denial of service. This issue has been patched in versions 3.3.10, 4.25.1, and 4.28.0.
Who should check
Teams running OWASP CRS v4 (up to 4.27.0) or v3.3 (up to 3.3.9) on ModSecurity v2 or v3 with PCRE2, including WAF operators in front of web apps
Not fixed by: Lowering SecPcreMatchLimit does not remove the detection bypass.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.8/10CVSS 8.8
- No patch0/5No signal
What would change the score
- Would score about 71 if added to CISA KEV
- Would score about 66 if CISA's SSVC rates exploitation active
- Would score about 31 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 3.3.10, 4.25.1, 4.28.0.
Workaround: Constrain request size (reduces exploitability but does not eliminate it)
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-61619 (OWASP CRS: ReDoS in shared unix-shell-evasion regex-assembly include (12 RCE rules) - PCRE2 backtracking-limit exhaustion causes detection…), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-61619 (entry last updated 2026-11-11):
Affected:
- coreruleset coreruleset: fixed in 3.3.10; fixed in 4.25.1; fixed in 4.28.0
Fixed versions: 3.3.10, 4.25.1, 4.28.0.
Conditions (all must be true for the bug to be hit):
- Deployments running CRS on ModSecurity v2 or v3 (PCRE2-based engines) (source: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg)
- Uses the affected unix-shell-evasion RCE rules in CRS v4 or the matching v3.3 rules (source: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, no user action.
Workaround: Constrain request size (reduces exploitability but does not eliminate it) (source: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg)
CISA KEV: CVE-2026-61619 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-61619 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg
- https://github.com/coreruleset/coreruleset/commit/4665b6d7a79a81aa8a802ef3c901d69491c009a4
- https://github.com/coreruleset/coreruleset/commit/6083611d00291e85ab7b587e96577deb53ed9cac
- https://github.com/coreruleset/coreruleset/commit/e3b612a909532dcc8d056c01ac04b31117b71505
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-61619
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-61619"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- coreruleset coreruleset
fixed in 3.3.10; fixed in 4.25.1; fixed in 4.28.0
Evidence 6
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 3
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-61619
Is CVE-2026-61619 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
The PCRE2 regex engine hits its backtracking limit on a crafted request, so the unix-shell-evasion RCE rule fails to evaluate for that request and the payload is not inspected. The same input can also use extra server CPU on each request.Source: github.com
Which versions are affected by CVE-2026-61619?
coreruleset: before 3.3.10; before 4.25.1; before 4.28.0.Source: cve.now feed data
Am I affected, and how do I check?
Deployments running OWASP CRS on ModSecurity v2 or v3 with PCRE2-based engines that use the affected unix-shell-evasion RCE rules in CRS v4, or the matching rules in v3.3. To check, look at the installed CRS version and whether the unix-shell-evasion rule files, generated from regex-assembly/include/unix-shell-evasion-prefix.ra, are loaded.Source: github.com
How do I fix CVE-2026-61619?
Upgrade to CRS 4.28.0, which contains the fix (main commit e3b612a9). As a workaround, constrain request size; this reduces the problem but does not eliminate it.Source: github.com