CVE-2026-9076
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk21th percentile - higher than 21% of all known CVEs
Summary
The vulnerability concerns the password-based CMS decryption process, which may lead to a heap out-of-bounds read. An attacker can choose the encryption algorithm, resulting in a potential error in the kek_unwrap_key() function.
Risk Assessment
If the error occurs, it may cause the application to crash, leading to a denial of service. There is no information disclosure as the over-read bytes are not revealed to the attacker.
Recommendation
It is recommended to avoid processing untrusted CMS data and to implement appropriate safeguards when selecting the encryption algorithm. Applications using the CMS_decrypt() function should also be monitored.
Original NVD description (English source)
Issue summary: When CMS password-based decryption (RFC 3211 / PWRI key unwrap) processes attacker-supplied CMS data, an attacker-chosen stream-mode KEK cipher can trigger a heap out-of-bounds read in kek_unwrap_key(). Impact summary: A heap buffer over-read may trigger a crash which leads to Denial of Service for an application if the input buffer ends at a memory page boundary and the following page is unmapped. There is no information disclosure as the over-read bytes are not revealed to the attacker. The key unwrapping function performs a check-byte test as specified in the RFC that reads 7 bytes from a heap allocation that is based on the wrapped key length from the message. There is a minimum length check based on the block length of the wrapping cipher. However the cipher is selected from an OID carried in the attacker's PWRI keyEncryptionAlgorithm with no requirement that the cipher be a block cipher. When an attacker selects a stream-mode cipher the guard will be ineffective and the allocated buffer containing the unwrapped key can be too small to fit the check-bytes specified in the RFC and a buffer over-read can happen. Applications calling CMS_decrypt() or CMS_decrypt_set1_password() (equivalently openssl cms -decrypt -pwri_password ...) on untrusted CMS data are vulnerable to this issue. No password knowledge is required: the over-read happens during the unwrap attempt before any authentication succeeds. The over-read is limited to a few bytes and is not written to output, so there is no information disclosure. Triggering a crash requires the allocation to border unmapped memory, which is unlikely with the normal allocator. The FIPS modules are not affected by this issue.