CVE-2025-40907

A flaw was found in the FCGI library. In affected versions, specially crafted nameLen or valueLen values in data sent to the IPC socket may result in a heap-based buffer overflow, which can cause an application crash or other undefined behavior. This occurs in ReadParams in fcgiapp.c.

This vulnerability is Important rather than just a Moderate flaw because it stems from an integer overflow in the allocation size calculation during parameter parsing in the FastCGI implementation. When the application processes incoming FastCGI parameters, it calculates the total size of memory to allocate by adding the name and value lengths along with two additional bytes. On 32-bit systems, this arithmetic operation can wrap around (due to the limited 32-bit size of size_t), leading to a significantly smaller allocation than intended. However, subsequent calls to FCGX_GetStr use the original (large) lengths provided by the attacker and write far beyond the allocated memory region (heap overflow). Unlike a moderate vulnerability (e.g., memory leak or a simple read out-of-bounds), this heap overflow directly allows an attacker to overwrite adjacent memory in the heap in a controlled way, potentially leading to arbitrary code execution, data corruption, or privilege escalation.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

No mitigation is currently available that meets Red Hat Product Security’s standards for usability, deployment, applicability, or stability.