CVE-2026-9076: Out-of-Bounds Read in CMS Password-Based Decryption

Synopsis

An out-of-bounds heap read in OpenSSL's CMS password-based decryption (the PWRI key-unwrap routine, kek_unwrap_key()) allows a network attacker to submit crafted CMS data that selects a stream-mode cipher where a block cipher is expected, causing the unwrap code to read a few bytes past the end of a heap allocation. No authentication is needed and no password knowledge is required because the over-read happens before any credential check. Successful exploitation crashes the affected application, resulting in denial of service; there is no data disclosure. Patched-image rebuilds at versions 1.0.2zq, 1.1.1zh, 3.0.21, 3.4.6, and 3.5.7 are available on HarborGuard for affected environments.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker submits malicious CMS data over the network to any application calling CMS_decrypt() or CMS_decrypt_set1_password() on untrusted input.

• AuthenticationNot required

  No credentials or password knowledge are required; the heap over-read occurs during the key-unwrap attempt before any authentication check.

• Victim interactionNot required

  No user action is needed; the application processes the attacker-supplied CMS data automatically upon receipt.

• Attack complexityDetail

  The exploit is straightforward and condition-free: the attacker simply supplies a CMS payload referencing a stream-mode cipher OID; no race conditions or environmental constraints are needed.

Blast Radius

• Crashes the process handling CMS decryption, taking down any service that calls CMS_decrypt() or CMS_decrypt_set1_password() on untrusted data.
• No data is read out by the attacker; the over-read bytes are consumed internally and not reflected in any response.
• Impact is limited to availability; confidentiality and integrity of stored data are not affected by this vulnerability.