WAF rule bypass via zero-padded HTML entities
Published Feb 25, 2025 · Updated Feb 26, 2025
Encoding error in OWASP ModSecurity libmodsecurity3 3.0.13 allows remote attackers to bypass WAF rules with zero-padded HTML entities. The t:htmlEntityDecode transformation uses fixed-buffer handling that leaves leading-zero decimal or hexadecimal entities improperly decoded instead of ignoring their padding. Exploitation requires a deployed rule to use that transformation; the crafted payload then reaches the protected application without the intended rule inspection.
Summary
What happened
Encoding error in OWASP ModSecurity libmodsecurity3 3.0.13 allows remote attackers to bypass WAF rules with zero-padded HTML entities. The t:htmlEntityDecode transformation uses fixed-buffer handling that leaves leading-zero decimal or hexadecimal entities improperly decoded instead of ignoring their padding. Exploitation requires a deployed rule to use that transformation; the crafted payload then reaches the protected application without the intended rule inspection.
The record
- CVE
- CVE-2025-27110
- Published
- Feb 25, 2025
- Updated
- Feb 26, 2025
- Vendor
- OWASP ModSecurity
- Product
- ModSecurity
- Classifications
- CWE-172, T1027
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Feb 25, 2025CVE publishedPublication date reported by the CVE source.
- Feb 26, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion== 3.0.13
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
- Zero-padded HTML entity bypass reproductionproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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