OpenSSL up to 4.0.1 CMS CMS_decrypt out-of-bounds write

Summaryinfo

A vulnerability marked as critical has been reported in OpenSSL up to 3.0.21/3.4.6/3.5.7/3.6.3/4.0.1. The affected element is the function CMS_decrypt of the component CMS. Performing a manipulation results in out-of-bounds write. This vulnerability is cataloged as CVE-2026-63072. It is possible to initiate the attack remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as critical, was found in OpenSSL up to 3.0.21/3.4.6/3.5.7/3.6.3/4.0.1. This affects the function CMS_decrypt of the component CMS. The manipulation with an unknown input leads to a out-of-bounds write vulnerability. CWE is classifying the issue as CWE-787. The product writes data past the end, or before the beginning, of the intended buffer. This is going to have an impact on integrity, and availability. The summary by CVE is:

Issue summary: OpenSSL CMS decryption sizes the key-unwrap output buffer based on querying the unwrapped key size, but the AES-WRAP-PAD unwrap primitive can write and cleanse more bytes than that query reports, causing an 8-byte out-of-bounds heap write. Impact summary: An attacker who supplies a crafted CMS message can trigger a deterministic 8-byte out-of-bounds heap write when the victim decrypts it with CMS_decrypt(), corrupting the heap and typically resulting in a Denial of Service. CWE: CWE-787: Out-of-bounds Write Description: The key-wrap OID is potentially attacker-controlled on the wire. CMS unwrapping allows both id-aesNNN-wrap-pad and id-aesNNN-wrap ciphers. An attacker can take a legitimate message and change a single OID byte to select the padded variant while leaving the message otherwise valid. Since the unwrap key is derived from the recipient's private operation (ECDH key agreement or ML-KEM decapsulation), the RFC 5649 integrity check cannot pass, and the decryption fails with integrity failure. The write is a fixed-size (8-byte), fixed-value (zero) heap overflow immediately past the allocation, requires no special configuration, and is reachable from the public CMS_decrypt() function. The consequence is a heap corruption leading to a Denial of Service. The fix in the CMS code sizes the unwrap output buffer for the worst case so a failed unwrap cannot write past the allocation. FIPS impact: no As the CMS code lives outside the FIPS module boundary, no FIPS modules are affected by this CVE.

The advisory is shared at openssl-library.org. This vulnerability is uniquely identified as CVE-2026-63072 since 07/15/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 08/25/2026).

Upgrading to version 1.1.1zi, 3.0.22, 3.4.7, 3.5.8, 3.6.4 or 4.0.2 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Network Encryption Software

Name

• OpenSSL

Version

• 3.0.0
• 3.0.1
• 3.0.2
• 3.0.3
• 3.0.4
• 3.0.5
• 3.0.6
• 3.0.7
• 3.0.8
• 3.0.9
• 3.0.10
• 3.0.11
• 3.0.12
• 3.0.13
• 3.0.14
• 3.0.15
• 3.0.16
• 3.0.17
• 3.0.18
• 3.0.19
• 3.0.20
• 3.0.21
• 3.4.0
• 3.4.1
• 3.4.2
• 3.4.3
• 3.4.4
• 3.4.5
• 3.4.6
• 3.5.0
• 3.5.1
• 3.5.2
• 3.5.3
• 3.5.4
• 3.5.5
• 3.5.6
• 3.5.7
• 3.6.0
• 3.6.1
• 3.6.2
• 3.6.3
• 4.0.0
• 4.0.1

License

• open-source

Website

• Product: https://www.openssl.org/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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