CVE-2026-124040
HighCVSS 8.1Exploitation Probability (EPSS)
Low risk44th percentile - higher than 44% of all known CVEs
Summary
CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free in handle_http2() that retains freed :method and :path pointers. An unauthenticated remote attacker can send a later HEADERS frame omitting these pseudo-headers to influence the request method or path seen by access rules, or crash the server.
Risk Assessment
An attacker could bypass access control rules by manipulating the request method or path, or cause a server crash. Only builds with HTTP/2 support are affected.
Recommendation
Upgrade CivetWeb beyond 1.16 or disable HTTP/2 (enable_http2) until a fix is available. Monitor logs for unusual HEADERS frames.
Other vulnerabilities in CivetWeb
See all- CVE-2026-29035Medium
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.
- CVE-2025-9648High
A vulnerability in the CivetWeb library's mg_handle_form_request function allows remote attackers to trigger a denial of service (DoS). Sending a specially crafted HTTP POST request containing a null byte in the payload causes the server to enter an infinite loop during form data parsing. Multiple malicious requests result in complete CPU exhaustion and render the service unresponsive.
- CVE-2025-55763High
Buffer Overflow in the URI parser of CivetWeb 1.14 through 1.16 (latest) allows a remote attacker to achieve remote code execution via a crafted HTTP request. This vulnerability is triggered during request processing and may allow an attacker to corrupt heap memory, potentially leading to denial of service or arbitrary code execution.
Original NVD description (English source)
CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free vulnerability in handle_http2() that retains freed :method and :path pointers. Unauthenticated remote attackers can send a later HEADERS frame omitting these pseudo-headers to influence request method or path seen by access rules, or crash the server.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS