WAF bypass via uninspected encoded multipart bodies
Published Sep 20, 2022 · Updated Nov 3, 2025
Detection bypass in OWASP Core Rule Set 3.0.x, 3.1.x, 3.2.1, and 3.3.2 allows remote attackers to evade multipart inspection. ModSecurity and CRS do not decode or inspect multipart bodies whose part-level Content-Type or Content-Transfer-Encoding headers select a character encoding. Exploitation requires a backend that decodes the selected encoding; malicious request content can then reach that backend without CRS detection.
Summary
What happened
Detection bypass in OWASP Core Rule Set 3.0.x, 3.1.x, 3.2.1, and 3.3.2 allows remote attackers to evade multipart inspection. ModSecurity and CRS do not decode or inspect multipart bodies whose part-level Content-Type or Content-Transfer-Encoding headers select a character encoding. Exploitation requires a backend that decodes the selected encoding; malicious request content can then reach that backend without CRS detection.
The record
- CVE
- CVE-2022-39956
- Published
- Sep 20, 2022
- Updated
- Nov 3, 2025
- Vendor
- OWASP Foundation
- Product
- OWASP Core Rule Set
- Classifications
- CWE-863, CWE-116, T1027
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 20, 2022CVE publishedPublication date reported by the CVE source.
- Nov 3, 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.x
- Affected versionversion=3.1.x
- Affected versionversion=unspecified <=3.2.1
- Affected versionversion=unspecified <=3.3.2
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.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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