CVE-2026-29035
CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression
CVSS Score
6.5
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-787 |
| Vendor | civetweb |
| Product | civetweb |
| Published | Aug 11, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
High
Affected Versions
civetweb / civetweb
0 ≤ 4a4f0c95
References
Credits
Kazuma Matsumoto, a security researcher at GMO Cybersecurity by IERAE, Inc.