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CVE-2026-29035— CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression

Quick assessment

Affected
civetweb civetweb
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

CivetWeb是civetweb组织开源的一个易于使用、功能强大、可嵌入 C/C++ 的 Web 服务器,具有可选的 CGI、SSL 和 Lua 支持。 CivetWeb 4a4f0c95版本存在缓冲区错误漏洞，该漏洞源于read_websocket()函数存在堆和栈缓冲区溢出，攻击者可通过协商permessage-deflate并发送设置RSV1位的特制压缩WebSocket帧，导致服务器越界写入zlib同步尾，造成堆元数据损坏、拒绝服务或潜在代码执行。

CVSS 6.5 · Medium EPSS 0.61% · P49

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
civetweb civetweb ≤ 4a4f0c95 affected
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I. Basic Information for CVE-2026-29035

Vulnerability Information
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Vulnerability Title
CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5
Vulnerability Title
CivetWeb 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
CivetWeb是civetweb组织开源的一个易于使用、功能强大、可嵌入 C/C++ 的 Web 服务器,具有可选的 CGI、SSL 和 Lua 支持。 CivetWeb 4a4f0c95版本存在缓冲区错误漏洞，该漏洞源于read_websocket()函数存在堆和栈缓冲区溢出，攻击者可通过协商permessage-deflate并发送设置RSV1位的特制压缩WebSocket帧，导致服务器越界写入zlib同步尾，造成堆元数据损坏、拒绝服务或潜在代码执行。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
civetweb civetweb 0 ~ 4a4f0c95 -

II. Public POCs for CVE-2026-29035

# POC Description Source Link Shenlong Link
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III. Intelligence Information for CVE-2026-29035

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Vendor Advisories for CVE-2026-29035 (1)

IV. Related Vulnerabilities

Same product: civetweb
Same vendor: civetweb
Same weakness: CWE-787