OpenSSL CMS NULL Deref (before 4.0) - DoS
CVE-2026-42766 Published on June 9, 2026
Possible NULL Dereference in Password-Based CMS Decryption
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.
Vulnerability Analysis
CVE-2026-42766 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
NULL Pointer Dereference
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions.
Products Associated with CVE-2026-42766
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Affected Versions
OpenSSL:- Version 4.0.0 and below 4.0.1 is affected.
- Version 3.6.0 and below 3.6.3 is affected.
- Version 3.5.0 and below 3.5.7 is affected.
- Version 3.4.0 and below 3.4.6 is affected.
- Version 3.0.0 and below 3.0.21 is affected.
- Version 1.1.1 and below 1.1.1zh is affected.
- Version 1.0.2 and below 1.0.2zq is affected.