ModSecurity: HTML decoder missing entities, leading to evasion
- Exploited
- No known exploitation
- Fix
- Fixed in 2.9.15, 3.0.17
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 2.9.15, 3.0.17.
- Last modified
- 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? →
- 23/100 · provisional
- 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
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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity6.3/10CVSS 6.3
- No patch0/5No signal
What would change the score
- Would score about 68 if added to CISA KEV
- Would score about 63 if CISA's SSVC rates exploitation active
- Would score about 28 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 2.9.15, 3.0.17.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- owasp-modsecurity ModSecurity
fixed in 2.9.15; From 3.0.0 · fixed in 3.0.17
Evidence 5
- Advisory
- Repository
- Repository
- Repository
- Repository
Corrections
None so far.
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Questions about CVE-2026-61812
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: cve.now feed data
Which versions are affected by CVE-2026-61812?
ModSecurity: before 2.9.15; from 3.0.0 before 3.0.17.Source: cve.now feed data
How do I fix CVE-2026-61812?
Upgrade to a fixed version: 2.9.15, 3.0.17.Source: cve.now feed data