CVE-2026-42771: Possible Out of Bounds Read in X509_VERIFY_PARAM_set1_email()
Issue summary: When the X509VERIFYPARAMset1email 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 X509VERIFYPARAM[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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Configuration
Disable calls to X509_VERIFY_PARAM_set1_email and X509_VERIFY_PARAM_add_email (i.e., disable email-based S/MIME email parameter setting/validation) in your application configuration or code until an OpenSSL fix is available.
Application using OpenSSL X509_VERIFY_PARAM_email_validation = disabled - Compensating control
Run S/MIME validation in an isolated/sandboxed process with restricted privileges and resource limits, and/or avoid performing S/MIME validation on untrusted email input. At mail gateways or preprocessors, block or reject messages with From: addresses that contain unusually long local-parts to reduce exposure to crafted inputs.
- Operational
Audit codepaths for any use of X509_VERIFY_PARAM_set1_email or X509_VERIFY_PARAM_add_email. If email-based verification must be performed before a patch is available, enforce the 64-octet local-part limit on email addresses prior to calling the OpenSSL functions, and add input validation/sanitization to prevent overly long or malformed local-part values.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-42771?
The severity of CVE-2026-42771 is medium with a CVSS score of 6.2.
What is the risk associated with CVE-2026-42771?
The risk associated with CVE-2026-42771 is rated at 37.
How do I fix CVE-2026-42771?
To fix CVE-2026-42771, update to the latest version of OpenSSL that contains the security patch.
What impact does CVE-2026-42771 have on applications?
CVE-2026-42771 can lead to an out of bounds read when validating crafted e-mail addresses, potentially affecting application stability.
In which function is the vulnerability CVE-2026-42771 found?
CVE-2026-42771 is found in the function X509_VERIFY_PARAM_set1_email().