CVE-2026-42771 Possible Out of Bounds Read in X509_VERIFY_PARAM_set1_email()

Medium 6.2 Published 9 Jun 2026 Updated 10 Jun 2026

An out-of-bounds read in OpenSSL's email validation can cause a crash, leading to denial of service during S/MIME message processing.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-42771?

CVE-2026-42771 is a medium-severity memory corruption vulnerability in Openssl Openssl, published on 9 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

Issue summary: When the X509_VERIFY_PARAM_set1_email is called by an application to validate a crafted e-mail address, such as during S/MIME message validation, an out of bounds read can happen.

Impact summary: This out of bounds read will not directly exfiltrate the data read to the attacker so the most likely result is a crash and a Denial of Service.

An internal helper function called from X509_VERIFY_PARAM_[set|add]_email() used a wrong length when validating the local part of an email address. This could cause the 64 octet limit on the local part of an email address to be not enforced, or cause an out of bound read and potentially a crash.

The bug is reachable via S-MIME validation with a crafted From: address supplied in an email message that can potentially cause a crash.

No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.

Weakness: CWE-125

Which versions are affected by CVE-2026-42771?

It affects 1 product.

Products include Openssl Openssl.

How do I fix CVE-2026-42771?

Apply the vendor's patch.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-42771 being exploited?

There is no known exploitation of CVE-2026-42771 in the wild and no public exploit code.

All Openssl Openssl vulnerabilities

Sources

Also known as GHSA-6fmj-jmjq-qcmg, UBUNTU-CVE-2026-42771.