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CVE-2026-124040

CivetWeb through 1.16 HTTP/2 Use-After-Free via Stale Pseudo-Header State

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.

CVSS 4.0 · 9.2 Critical EPSS < 1% KEV · Not listed
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CVE-2026-29035

CivetWeb Heap/Stack Buffer Overflow via WebSocket permessage-deflate Decompression

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.

CVSS 4.0 · 8.3 High EPSS < 1% KEV · Not listed
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CVE-2026-5789

Search path without quotes in CivetWeb

Vulnerability related to an unquoted search path in CivetWeb v1.16. This vulnerability allows a local attacker to execute arbitrary code with elevated privileges by placing a malicious executable in a directory that is scanned before the intended application path (C:\Program Files\CivetWeb\CivetWeb.exe --), due to the absence of quotes in the service configuration.

CVSS 4.0 · 8.5 High EPSS < 1% KEV · Not listed
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CVE-2025-9648

Denial of Service in CivetWeb

A vulnerability in the CivetWeb library's function mg_handle_form_request allows remote attackers to trigger a denial of service (DoS) condition. By sending a specially crafted HTTP POST request containing a null byte in the payload, the server enters an infinite loop during form data parsing. Multiple malicious requests will result in complete CPU exhaustion and render the service unresponsive to further requests. This issue was fixed in commit 782e189. This issue affects only the library, standalone executable pre-built by vendor is not affected.

CVSS 4.0 · 8.7 High EPSS < 1% KEV · Not listed
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CVE-2025-55763

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.

CVSS 3.1 · 7.5 High EPSS 1.2% KEV · Not listed
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CVE-2020-27304

civetweb: directory traversal when using the built-in example HTTP form-based file upload mechanism via the mg_handle_form_request API

The CivetWeb web library does not validate uploaded filepaths when running on an OS other than Windows, when using the built-in HTTP form-based file upload mechanism, via the mg_handle_form_request API. Web applications that use the file upload form handler, and use parts of the user-controlled filename in the output path, are susceptible to directory traversal

CVSS 3.1 · 9.8 Critical EPSS 3.3% KEV · Not listed
CVE-2018-12684

civetweb: Out-of-bounds read in civetweb.c:send_ssi_file() allows attackers to cause denial of service or information disclosure

Out-of-bounds Read in the send_ssi_file function in civetweb.c in CivetWeb through 1.10 allows attackers to cause a Denial of Service or Information Disclosure via a crafted SSI file.

CVSS 3.0 · 7.1 High EPSS 1.0% KEV · Not listed
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