Vulnerability · Published Aug 11, 2026 · Assigned by VulnCheck
CVE-2026-29035CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression
Medium 6.5
In plain English
A medium-severity out-of-bounds write in civetweb from civetweb. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities).
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | civetweb | no fix listed | DEBIAN-CVE-2026-29035 |
| Debian:13 | civetweb | no fix listed | DEBIAN-CVE-2026-29035 |
| Debian:14 | civetweb | no fix listed | DEBIAN-CVE-2026-29035 |
| Ubuntu:22.04:LTS | civetweb | no fix listed | UBUNTU-CVE-2026-29035 |
| Ubuntu:24.04:LTS | civetweb | no fix listed | UBUNTU-CVE-2026-29035 |
| Ubuntu:26.04:LTS | civetweb | no fix listed | UBUNTU-CVE-2026-29035 |
Affected products (as reported)
Weakness: CWE-787 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H