# CVE-2026-118177: Calendar discovery accepted local file and remote network share locations

Status: published. Published: 2026-10-27. Updated: 2026-11-04.

When looking for calendars in a directory on a server, during account setup or when adding a new network calendar, Thunderbird accepted calendar locations pointing to other servers, local files or network shares. A malicious server, or a network attacker when the lookup used plain HTTP, could make Thunderbird subscribe to such a location. On Windows this could leak the user's NTLM credentials to an attacker-controlled host on every calendar refresh, and changes to the calendar could be written to the attacker's share or overwrite a local file. This vulnerability was fixed in Thunderbird 159 and Thunderbird 153.6.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Mozilla / Thunderbird: ≥ 153.6; ≤ 153.* (unaffected, rpm); ≥ 159; ≤ * (unaffected, rpm). Source: CNA: mozilla

## Severity and prioritization

- CVSS 3.1: 9.1 (critical); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H; source: ADP: CISA-ADP

- CVSS 3.1: 9.1 (critical); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H; source: NVD: 134c704f-9b21-4f2e-91b3-4a467353bcc0

- CISA KEV: No listing in collected sources

- EPSS: 0.18% as of 2026-11-04; percentile 7.58%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-601

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://bugzilla.mozilla.org/show_bug.cgi?id=2080924 (CNA: mozilla)

- https://www.mozilla.org/security/advisories/mfsa2026-121/ (CNA: mozilla)

- https://www.mozilla.org/security/advisories/mfsa2026-122/ (CNA: mozilla)

- https://bugzilla.mozilla.org/show_bug.cgi?id=2080924 (security@mozilla.org)

- https://www.mozilla.org/security/advisories/mfsa2026-121/ (security@mozilla.org)

- https://www.mozilla.org/security/advisories/mfsa2026-122/ (security@mozilla.org)

## Provenance

- CNA: mozilla: https://www.cve.org/CVERecord?id=CVE-2026-118177; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-118177; retrieved 2026-11-04; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-118177; retrieved 2026-11-04; source updated Not reported

Revision: 3449be98ef9d352964189d24e7b6cafdfc1130ab767621e0d172c1acf7931a23

Canonical: https://y2.dev/cve/CVE-2026-118177

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