{"cve":"CVE-2021-23991","nvd":{"published":"2021-06-24T14:15:09.197","modified":"2026-06-17T03:39:07.293","status":"Modified","description":"If a Thunderbird user has previously imported Alice's OpenPGP key, and Alice has extended the validity period of her key, but Alice's updated key has not yet been imported, an attacker may send an email containing a crafted version of Alice's key with an invalid subkey, Thunderbird might subsequently attempt to use the invalid subkey, and will fail to send encrypted email to Alice. This vulnerability affects Thunderbird < 78.9.1.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N","score":6.8},"cwes":[],"references":["https://bugzilla.mozilla.org/show_bug.cgi?id=1673240","https://www.mozilla.org/security/advisories/mfsa2021-13/","https://bugzilla.mozilla.org/show_bug.cgi?id=1673240","https://www.mozilla.org/security/advisories/mfsa2021-13/"],"products":["mozilla:thunderbird"],"source":"nvd","synced_at":"2026-10-19T21:20:07.141963181+00:00"},"epss":{"cve":"CVE-2021-23991","score":0.01035,"percentile":0.63893,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}