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The vulnerability CVE-2025-11931 in wolfSSL involves an integer underflow in the XChaCha20-Poly1305 decryption function. Specifically, when the function wc_XChaCha20Poly1305_Decrypt() is called, an integer underflow occurs during the calculation of buffer sizes or offsets. This underflow leads to out-of-bounds memory access, potentially allowing an attacker to read or write beyond the allocated memory boundaries. The issue arises due to improper validation of input parameters, such as the length of ciphertext or associated data. When a maliciously crafted input is provided, the subtraction operation results in a negative value that wraps around to a large positive number due to unsigned integer representation. This causes the subsequent memory operations to access data outside the intended buffer, leading to information disclosure, corruption, or possible code execution. The vulnerability is exploitable only through direct application calls to this function, as it is not used in TLS connections, limiting the attack surface. However, applications that use XChaCha20-Poly1305 for encryption and decryption via wolfSSL’s API are at risk. The underflow likely occurs in the Poly1305 authentication tag verification or during the XChaCha20 decryption process. Attackers could exploit this by sending crafted packets to trigger the underflow, potentially bypassing authentication or causing a denial of service. Detailed analysis shows that the underflow happens when the input length is less than the Poly1305 tag size, causing a subtraction to underflow. This leads to incorrect pointer arithmetic and out-of-bounds read or write. The vulnerability is critical because it can compromise the confidentiality and integrity of encrypted data. WolfSSL has acknowledged the issue and is working on a patch.
Platform: wolfSSL
Version: Multiple versions
Vulnerability: Integer underflow out-of-bounds access
Severity: Critical
Date: 11/21/2025
Prediction: Expected patch 12/2025
What Undercode Say:
Analytics:
wolfssl-config –version
check security updates
scan for vulnerable code
code snippet: wc_XChaCha20Poly1305_Decrypt()
compile with wolfSSL flags
grep for function usage
analyze buffer sizes
debug with gdb
how Exploit:
Craft malicious ciphertext
Trigger integer underflow
Bypass authentication mechanisms
Read out-of-bounds memory
Execute arbitrary code
Denial of service attack
Exploit direct API calls
Use small input lengths
Protection from this CVE:
Update wolfSSL library
Avoid direct decryption calls
Validate input parameters
Use TLS connections instead
Monitor for patches
Implement boundary checks
Disable vulnerable function
Apply security fixes
Impact:
Data confidentiality compromised
Integrity loss possible
Code execution risk
System crash potential
Authentication bypass
Memory corruption issues
Application vulnerability
Requires immediate patching
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Sources:
Reported By: nvd.nist.gov
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