CVE-2025-9648: 
Linux Debian vulnerability analysis and mitigation

A vulnerability (CVE-2025-9648) was discovered in the CivetWeb library's function mghandleform_request that allows remote attackers to trigger a denial of service (DoS) condition. The vulnerability was disclosed on September 29, 2025, affecting all versions of CivetWeb library before version 1.08. When a specially crafted HTTP POST request containing a null byte in the payload is sent, the server enters an infinite loop during form data parsing (CERT.PL, NVD).

The vulnerability is classified as CWE-158 (Improper Neutralization of Null Byte or NUL Character). The issue occurs in the mghandleform_request function when processing form data. Multiple malicious requests will result in complete CPU exhaustion and render the service unresponsive. The vulnerability has received a CVSS v4.0 score of 8.7 (HIGH) with the vector string CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N (NVD).

The primary impact of this vulnerability is the potential for denial of service attacks against systems using the CivetWeb library. When exploited, the vulnerability can cause complete CPU exhaustion, making the service unresponsive to further requests. Notably, this issue only affects applications using the library directly, while the standalone executable pre-built by the vendor is not affected (CERT.PL).

The vulnerability has been fixed in commit 782e189 of the CivetWeb repository. The fix includes additional validation to reject requests that violate URL encoding standards and prevents the infinite loop condition. Users are advised to update to the patched version of the library (GitHub Commit).