Security readout for executives and security teams
Plain-English summary
This flaw lets some multipart HTTP requests pass through OWASP ModSecurity CRS without the relevant request content being decoded and inspected. If the protected application later understands that encoding, an attacker may get malicious input past the WAF. It is a high-priority WAF coverage gap, not evidence of compromise by itself.
Executive priority
Treat this as a high-priority remediation for internet-facing services relying on ModSecurity CRS as a primary control. Prioritize systems handling uploads, forms, or APIs with multipart requests. There is no supplied evidence of active exploitation, but the bypass can weaken defenses in front of vulnerable applications.
Technical view
CVE-2022-39956 is a partial CRS rule-set bypass affecting multipart requests using character encoding in Content-Type or deprecated Content-Transfer-Encoding multipart MIME headers. CRS may not decode and inspect the multipart body, while a backend that supports the encoding may process it. Affected CRS branches include 3.0.x, 3.1.x, 3.2.1, and 3.3.2.
Likely exposure
Exposure is most likely where OWASP ModSecurity CRS protects public web applications that accept multipart requests, especially upload or form endpoints, and backends support the encoded multipart content. The source bundle names CRS versions 3.0.x, 3.1.x, 3.2.1, and 3.3.2 as affected.
Exploitation context
The CVE is not listed as KEV in the supplied bundle, and no cited source states active exploitation. Practical risk depends on whether attackers can reach multipart endpoints and whether the backend decodes content the WAF did not inspect.
Researcher notes
The key condition is parser mismatch: CRS inspection may miss encoded multipart content that the backend accepts. The bundle does not prove all backends are exploitable, and it does not provide active exploitation evidence. Validation should focus on exact CRS and ModSecurity versions, reachable multipart endpoints, and backend decoding behavior.
Mitigation direction
- Upgrade CRS 3.2.x deployments to 3.2.2 or later.
- Upgrade CRS 3.3.x deployments to 3.3.3 or later.
- Ensure ModSecurity is at least v2.9.6 or v3.0.8, per source guidance.
- Review Fedora, Debian, Gentoo, or other vendor package advisories for fixed builds.
- Check current OWASP CRS and ModSecurity guidance before deploying compensating controls.
Validation and detection
- Inventory all ModSecurity CRS deployments and record exact CRS versions.
- Confirm the installed ModSecurity engine version on each WAF host.
- Identify public multipart upload and form endpoints behind CRS.
- Verify backend frameworks do not process encodings the WAF misses.
- Use benign vendor or internal regression tests to confirm multipart inspection behavior.
- Confirm package updates align with distribution security advisories.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-863: Authorization and privilege behavior lookup
Authorization weaknesses can support privilege escalation and valid-account review, depending on exploit path. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2022-39956 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L3.93.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.3HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://coreruleset.org/20220919/crs-version-3-3-3-and-3-2-2-covering-several-cves/CVE reference
- FEDORA-2022-90708b46e3CVE reference · vendor-advisory
- FEDORA-2022-85a85c84b3CVE reference · vendor-advisory
- FEDORA-2022-1fd73a5285CVE reference · vendor-advisory
- [debian-lts-announce] 20230130 [SECURITY] [DLA 3293-1] modsecurity-crs security updateCVE reference · mailing-list
- GLSA-202305-25CVE reference · vendor-advisory
- https://lists.debian.org/debian-lts-announce/2025/08/msg00004.htmlCVE reference
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Incorrect Authorization
Incorrect Authorization represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.