CVE-2025-63095: Crafty Input Cripples Tempus Ex’s hello-video-codec

Overview

CVE-2025-63095 details a Denial of Service (DoS) vulnerability found in version 0.1.0 of the Tempus Ex hello-video-codec. The vulnerability stems from insufficient input validation within the BitstreamWriter::write_bits() function. A malicious actor can exploit this flaw by providing crafted input that triggers a resource exhaustion or other condition leading to service disruption.

Technical Details

The root cause of the vulnerability lies in the BitstreamWriter::write_bits() function, specifically the lack of proper bounds checking or sanitization of the input it receives. The vulnerable code (at commit 3e9551c699311ea12ad7f2fce9562fbc990d524c) does not adequately verify the size or format of the data being written to the bitstream. By providing unexpected or excessively large values, an attacker can cause the application to consume excessive memory, enter an infinite loop, or crash entirely.

Example scenario (hypothetical, based on the description):

        
        // Hypothetical example based on the vulnerability description
        fn write_bits(data: u32, num_bits: u32) {
          // Vulnerable code - no bounds checking on num_bits
          if num_bits > 32 {
             //Potential crash
             panic!("Too many bits")
          }

          // write 'num_bits' bits from 'data' to the bitstream
          //...implementation...
        }
        
        

Without proper validation, an attacker can supply a very large num_bits value, potentially leading to out-of-bounds writes or calculations, triggering the DoS.

CVSS Analysis

Currently, there is no CVSS score available for CVE-2025-63095. However, based on the description of a Denial of Service vulnerability, it’s likely to receive a score in the medium to high range, depending on the ease of exploitation and the impact on availability. A medium score might be given if local access is required, while a high score is likely if the vulnerability is remotely exploitable.

Possible Impact

The exploitation of CVE-2025-63095 can have significant consequences. A successful attack can lead to:

• Service disruption: The primary impact is the unavailability of the service using the affected hello-video-codec. This could affect video playback, encoding, or other video processing functionalities.
• Resource exhaustion: The vulnerable function may consume excessive CPU or memory resources, impacting the performance of the entire system.
• Potential for further exploitation: While primarily a DoS, the initial vulnerability might be a stepping stone for further exploitation if combined with other vulnerabilities.

Mitigation or Patch Steps

To mitigate CVE-2025-63095, the following steps should be taken:

1. Update to a patched version: Check the Tempus Ex hello-video-codec repository for a patched version of the library that addresses the input validation issue in the BitstreamWriter::write_bits() function. Apply the update as soon as it becomes available.
2. Implement input validation: If a patch is not immediately available, implement robust input validation in your application to ensure that the num_bits parameter passed to BitstreamWriter::write_bits() is within acceptable bounds (e.g., less than or equal to 32).
3. Rate Limiting: Implement rate limiting to restrict the number of requests processed from single entity in defined time frame.

Applying the correct validation is critical for preventing malicious or malformed input data from crippling the application.

References

• CVE-2025-63095 GIST
• Tempus Ex hello-video-codec Repository
• Vulnerable Code (bitstream.rs)
• Specific Commit of Vulnerable Code