CVE-2026-118174

A flaw was found in Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: When a message containing an OpenPGP key attachment was displayed, Thunderbird automatically loaded the attachment's content to offer importing the key. A sender could mark the attachment as an external attachment pointing to an arbitrary URL, which Thunderbird then loaded without any user interaction, bypassing remote content blocking. On Windows, a URL pointing to an attacker-controlled network share could leak the user's NTLM credentials.

The NTLM credential leak only affects Thunderbird on Windows. On other operating systems, the issue allowed a remote request that bypassed remote content blocking.

Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

--- CME Mitigation Guidance (2026-11-03) --- Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.

The highest-value action is to prevent Thunderbird from automatically fetching external URLs when parsing OpenPGP key attachments upon message display: upgrade to Thunderbird 159 or 153.6 (or the fixed Thunderbird builds), which prevent automatic loading of external URL attachments when displaying messages containing OpenPGP keys, closing all 2 injection vectors (external OpenPGP key attachment with arbitrary URL, external OpenPGP key attachment pointing to an attacker-controlled network share). Until patched, this is a concern on Thunderbird deployments across all platforms, with NTLM credential leakage specifically impacting Windows hosts, so avoid displaying untrusted email messages and restrict egress traffic to external SMB shares and untrusted remote hosts. As a compensating measure, block outbound network connections to unauthorized external hosts to prevent external URL retrieval and contain NTLM hash exfiltration over outbound SMB. These controls limit blast radius and contain exploitation, but they do not fix the underlying server-side request forgery defect — apply the upstream patch to fully remediate.

Highest-impact CME: CME-1304 SSRF Prevention (Outbound Request Allowlist) (high)