CVE-2026-42766: Possible NULL Dereference in Password-Based CMS Decryption

Severity: medium (CVSS 5.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-09 · updated 2026-07-23
Weakness: CWE-476

Description

Issue summary: A specially crafted password-encrypted CMS message can trigger a NULL pointer dereference during CMS decryption. Impact summary: This NULL pointer dereference leads to an application crash and a Denial of Service. The CMS PasswordRecipientInfo.keyDerivationAlgorithm field is defined as OPTIONAL in the ASN.1 specification and may therefore be absent in specially crafted inputs. During the password-based CMS decryption the OpenSSL CMS implementation dereferences this field without first checking whether it was present. An attacker who supplies such a CMS message to an application performing password-based CMS decryption can trigger an application crash, leading to a Denial of Service. Applications that process password-encrypted CMS messages may be affected. The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

Affected products

OpenSSL: from 1.0.2 before 1.0.2zq; from 1.1.1 before 1.1.1zh; from 3.0.0 before 3.0.21; from 3.4.0 before 3.4.6; from 3.5.0 before 3.5.7; from 3.6.0 before 3.6.3 — fixed in 1.0.2zq, 1.1.1zh, 3.0.21, 3.4.6, 3.5.7, 3.6.3

How to fix

Upgrade to a fixed version: OpenSSL 1.0.2zq, 1.1.1zh, 3.0.21, 3.4.6. Check the vendor advisory for mitigations.

References

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