Full Report
Improper Neutralization of NUL Character vulnerability (CVE-2025-9648) has been found in CivetWeb software.
Analysis Summary
# Vulnerability: Improper Neutralization of NUL Character in CivetWeb
## CVE Details
- CVE ID: CVE-2025-9648
- CVSS Score: Unknown (Severity not explicitly provided, but DoS impact suggests High)
- CWE: CWE-158 (Improper Neutralization of Null Byte or NUL Character)
## Affected Systems
- Products: CivetWeb software (Library only)
- Versions: All versions before 1.08
- Configurations: Affects the library component when processing HTTP POST requests containing form data. Note: Standalone executable pre-built by the vendor is *not* affected.
## Vulnerability Description
The vulnerability resides in the CivetWeb library's `mg_handle_form_request` function. A remote attacker can trigger a Denial of Service (DoS) by sending a maliciously crafted HTTP POST request that includes a null byte (`\x00`) within the form data payload. The presence of the null byte causes the server to enter an infinite loop during the form data parsing process, leading to CPU exhaustion and service unavailability.
## Exploitation
- Status: Unknown (No specific report of in-the-wild exploitation, but a PoC mechanism exists via crafted HTTP requests)
- Complexity: Low (Triggered via a specially crafted network request)
- Attack Vector: Network
## Impact
- Confidentiality: No direct impact stated
- Integrity: No direct impact stated
- Availability: Severe (Denial of Service leading to complete CPU exhaustion)
## Remediation
### Patches
- The issue was fixed in commit 782e189 of the CivetWeb source code. Users should upgrade to version 1.08 or later (or apply the fix from the specified commit).
### Workarounds
- As the standalone executable pre-built by the vendor is reportedly not affected, ensure that the application is running the standalone executable rather than relying solely on the vulnerable library component, if possible.
- Implement network-level ingress filtering to block HTTP POST requests containing null bytes (`\x00`) if immediate patching is not feasible.
## Detection
- Indicators of compromise: High CPU utilization spikes correlated with periods of receiving HTTP POST traffic.
- Detection methods and tools: Network monitoring tools examining HTTP payloads for the presence of the NULL byte (`\x00`) within POST requests directed at the CivetWeb processing endpoints.
## References
- Vendor advisory: CERT Polska Report (29 September 2025)
- Relevant links:
- hxxps://www.cve.org/CVERecord?id=CVE-2025-9648
- hxxps://incydent.cert.pl/#!/lang=en
- hxxps://cert.pl/en/publications/