CVE-2026-42766 Possible NULL Dereference in Password-Based CMS Decryption
An attacker can cause a denial of service by sending a crafted password-encrypted CMS message to applications using OpenSSL for decryption.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42766?
CVE-2026-42766 is a medium-severity vulnerability in Openssl Openssl, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-476
Which versions are affected by CVE-2026-42766?
It affects 1 product.
Products include Openssl Openssl.
How do I fix CVE-2026-42766?
Apply the vendor's patch.
Is CVE-2026-42766 being exploited?
There is no known exploitation of CVE-2026-42766 in the wild and no public exploit code.
Other vulnerabilities in Openssl Openssl
Sources
Also known as ALPINE-CVE-2026-42766, AZL-89805, AZL-89867, AZL-89943, BELL-CVE-2026-42766, DEBIAN-CVE-2026-42766 and 5 more.