Bypass of remote UNC path restriction in mailbox: URLs

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-118176
StatePUBLISHED
Assignermozilla
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-27 19:17:29 UTC
Updated2026-10-27 19:17:29 UTC
DescriptionThunderbird's check that prevents mailbox: URLs from accessing files on remote Windows network shares could be bypassed using extended-length UNC paths. Displaying a specially crafted email could cause Thunderbird to connect to an SMB server chosen by the attacker, disclosing the user's Windows account name and NTLM authentication data, which could be used for offline password cracking or relay attacks. This bug only affects Thunderbird on Windows. Other operating systems are unaffected. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mozilla Thunderbird unaffected 153.6 153.* rpm Not specified
CNA Mozilla Thunderbird unaffected 159 * rpm Not specified

References

ReferenceSourceLinkTags
bugzilla.mozilla.org/show_bug.cgi [email protected] bugzilla.mozilla.org
www.mozilla.org/security/advisories/mfsa2026-122 [email protected] www.mozilla.org
www.mozilla.org/security/advisories/mfsa2026-121 [email protected] www.mozilla.org
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: YuYoung Sung (en)

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