CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- High
- Attack requirements
- None
- Impact type
- —
- Confidentiality · integrity · availability
- None · Low · High
- Fix status
- No fix listed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA.
Summary
CivetWeb (commit 4a4f0c95) contains a heap and stack buffer overflow vulnerability in the read_websocket() function that allows unauthenticated remote attackers to corrupt memory by sending compressed WebSocket frames when both USE_ZLIB and MG_EXPERIMENTAL_INTERFACES are defined. Attackers can negotiate permessage-deflate during the WebSocket handshake and send a crafted frame with the RSV1 bit set, causing the server to write a 4-byte zlib sync trailer out-of-bounds past the allocated buffer, leading to heap metadata corruption, denial of service, or potential code execution.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
Remediation
No fixed version listed by the sources yet.
Vendor assessments
Timeline
- 2026-10-02 Threatist record created from CVE-2026-29035
- 2026-10-03 Alias added: GHSA-xvrx-cw3m-h23c
References
Other 1
More CivetWeb vulnerabilities
- TI-2025-08840 Denial of Service in CivetWeb CVSS 4.0HIGH 8.7
- TI-2026-86093 Use-after-free in CivetWeb HTTP/2 pseudo-header handling CVSS 4.0CRITICAL 9.2
Sources
- CVE-2026-29035 · CVE Program
- CVE-2026-29035 · NVD
- FIRST EPSS
- GHSA-xvrx-cw3m-h23c · GitHub Advisory Database · CC BY 4.0
- CVE-2026-29035 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences