CVE-2026-92240 Mozilla CVE debrief

Who should care

Thunderbird users and administrators should assess exposure and apply patches due to the critical severity of this vulnerability. The vulnerability can cause denial-of-service due to application crashes, and exposure to malicious or compromised IMAP servers. Operators, platform administrators, and security teams should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance. They should also plan vendor

Why it matters

Defenders should prioritize verifying exposure and applying patches due to the critical severity and potential for denial-of-service in Thunderbird's IMAP response parser.

• Potential denial-of-service due to application crashes
• Exposure to malicious or compromised IMAP servers
• Need for verification of Thunderbird versions and configurations
• Priority for patching and updating Thunderbird installations

Technical summary

The vulnerability is caused by an out-of-bounds read in the IMAP response parser, which can be triggered by an untagged '* ID' response from a malicious or compromised IMAP server. This issue is reachable before authentication and can cause denial-of-service due to application crashes. The affected product context includes Thunderbird versions prior to 156, 140.16, and 153.3. Defenders should prioritize verifying exposure and applying patches due to the critical severity and potential for denial-of-service. The vulnerability was addressed in multiple Mozilla security advisories.

Defensive priority

Defenders should prioritize verifying exposure and applying patches due to the critical severity and potential for denial-of-service.

Recommended defensive actions

• Verify exposure by checking Thunderbird versions and configurations
• Apply patches to upgrade to Thunderbird 156, Thunderbird 140.16, or Thunderbird 153.3
• Monitor IMAP server configurations and authentication mechanisms
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The vulnerability was reported via Bugzilla and addressed in multiple Mozilla security advisories (MFSA 2026-94, MFSA 2026-95, MFSA 2026-96). The CVE record was published on 2026-09-15T20:19:41.677Z and has not been modified since then. The vulnerability affects Thunderbird versions prior to 156, 140.16, and 153.3. There is no information on known or unknown affected scope beyond these versions.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.