Overview
CVE-2025-11931 is a security vulnerability affecting the XChaCha20-Poly1305 decryption function within wolfSSL. Specifically, an integer underflow can occur during the decryption process when the wc_XChaCha20Poly1305_Decrypt() function is called directly by an application. Importantly, this vulnerability is not exploitable through TLS connections, as the affected function is not used in that context. The vulnerability was published on 2025-11-21. This article provides a technical breakdown of the issue, its potential impact, and recommended mitigation strategies.
Technical Details
The core of CVE-2025-11931 lies in a potential integer underflow within the wc_XChaCha20Poly1305_Decrypt() function. An integer underflow occurs when an arithmetic operation results in a value smaller than the minimum value that the data type can hold. In this case, a calculation within the decryption routine can potentially result in a negative value that is then interpreted as a very large positive number due to the wrap-around effect. This, in turn, leads to an out-of-bounds memory access when the code attempts to read or write data based on this incorrect length or offset. This could cause a crash or, in certain circumstances, lead to information disclosure or other malicious behavior.
CVSS Analysis
At the time of this writing, CVE-2025-11931 has a CVSS score of N/A. This is because a complete CVSS score calculation requires further analysis to determine the exploitability and impact with more precision. While the potential for an out-of-bounds access exists, the specific conditions required to trigger the underflow and the resulting impact need to be carefully assessed. Factors such as the calling context, the specific input values, and the system architecture all influence the final severity rating.
Possible Impact
The potential impact of CVE-2025-11931 includes:
- Denial of Service (DoS): The out-of-bounds access could lead to a crash, causing the affected application to terminate.
- Information Disclosure: Under certain conditions, the vulnerability might allow an attacker to read sensitive data from memory beyond the intended boundaries.
- Potential for Code Execution: Although less likely, in more complex scenarios, an attacker might be able to leverage the out-of-bounds access to inject and execute arbitrary code. This is highly dependent on the specific implementation and memory layout.
It’s crucial to emphasize that because the vulnerable function is only called directly by the application (and not by TLS), the attack surface is limited to specific applications that use wolfSSL and directly call the vulnerable function.
Mitigation or Patch Steps
The recommended mitigation strategy is to update to a patched version of wolfSSL that addresses CVE-2025-11931. Check the wolfSSL website or contact their support for the latest available patches. If patching is not immediately feasible, carefully review all code that calls wc_XChaCha20Poly1305_Decrypt() and implement input validation to prevent potential integer underflow conditions. Specifically, ensure that input lengths and offsets are carefully checked to prevent negative values during calculations within the decryption routine.
References
wolfSSL Pull Request #9223
wolfSSL Official Website
NIST NVD CVE-2025-11931 Entry (When Available)
