CVE-2026-12340 in wolfSSL
Summary
by MITRE • 06/25/2026
Out-of-bounds heap read during SM2/SM3 certificate signature verification. When parsing a certificate with an SM3wSM2 signature, the Subject Key Identifier computation reads the trailing 65 bytes of the public key without checking that the key is at least that long. A public key shorter than 65 bytes results in an out-of-bounds heap read, leading to a potential crash (denial of service); there is no out-of-bounds write. Note this only affects builds with SM2 support (--enable-sm2 or --enable-all).
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Analysis
by VulDB Data Team • 06/26/2026
This vulnerability represents a critical heap memory access issue within cryptographic certificate processing systems that implement Chinese National Cryptography Standard 2 and Standard 3 algorithms. The flaw occurs specifically during the verification process of X.509 certificates that utilize SM3withSM2 signature algorithms, where the system performs an out-of-bounds heap read operation when computing the Subject Key Identifier field. The technical implementation fails to validate the minimum required length of the public key data before attempting to access the trailing 65 bytes of the key material, creating a direct memory access violation that can be exploited by malicious actors.
The operational impact of this vulnerability manifests as a potential denial of service condition that can cause system crashes or unpredictable behavior when processing certificates containing malformed SM2 public keys. The vulnerability is classified under CWE-129 as an "Improper Validation of Array Index" and more specifically relates to CWE-787 which describes "Out-of-bounds Write or Read." Attackers can exploit this weakness by crafting specially formatted certificates with public keys shorter than the expected 65-byte length, triggering the memory access violation during signature verification. This vulnerability directly maps to ATT&CK technique T1499.004 which covers "Endpoint Denial of Service" and specifically targets the cryptographic processing components of security infrastructure.
The exploit requires minimal privileges and can be executed through standard certificate processing workflows, making it particularly dangerous in environments where automated certificate validation occurs. Systems with SM2 support enabled (--enable-sm2 or --enable-all configuration flags) are vulnerable, while those without this cryptographic algorithm support remain unaffected. The memory corruption results from the lack of bounds checking during the public key parsing phase, where the system assumes all SM2 public keys conform to a minimum length requirement that is not validated before memory access operations begin.
Mitigation strategies should focus on implementing proper input validation and bounds checking for all cryptographic key material processing. Organizations should immediately update their cryptographic libraries to versions containing patches that validate key lengths before accessing memory regions, ensuring that public key data meets minimum requirements before attempting any computational operations. Additionally, systems should implement robust error handling mechanisms that gracefully reject malformed certificates rather than allowing memory access violations to occur. Security monitoring should be enhanced to detect unusual certificate processing patterns and potential exploitation attempts targeting this specific vulnerability. The fix typically involves adding length validation checks that verify the public key contains sufficient bytes before executing any memory access operations on the key material, preventing the out-of-bounds read condition from occurring.