{"api_version":"1","generated_at":"2026-04-23T01:15:01+00:00","cve":"CVE-2021-29991","urls":{"html":"https://cve.report/CVE-2021-29991","api":"https://cve.report/api/cve/CVE-2021-29991.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2021-29991","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2021-29991"},"summary":{"title":"CVE-2021-29991","description":"Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two separate headers. This allowed for a header splitting attack against servers using HTTP/3. This vulnerability affects Firefox < 91.0.1 and Thunderbird < 91.0.1.","state":"PUBLIC","assigner":"security@mozilla.org","published_at":"2021-11-03 01:15:00","updated_at":"2021-11-04 21:01:00"},"problem_types":["CWE-444"],"metrics":[],"references":[{"url":"https://www.mozilla.org/security/advisories/mfsa2021-37/","name":"https://www.mozilla.org/security/advisories/mfsa2021-37/","refsource":"MISC","tags":[],"title":"Security Vulnerabilities fixed in Firefox 91.0.1 and Thunderbird 91.0.1 — Mozilla","mime":"text/html","httpstatus":"200","archivestatus":"200"},{"url":"https://bugzilla.mozilla.org/show_bug.cgi?id=1724896","name":"https://bugzilla.mozilla.org/show_bug.cgi?id=1724896","refsource":"MISC","tags":[],"title":"Access Denied","mime":"text/html","httpstatus":"200","archivestatus":"404"},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-29991","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-29991","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[{"cve_year":"2021","cve_id":"29991","vulnerable":"1","versionEndIncluding":"","cpe1":"cpe","cpe2":"2.3","cpe3":"a","cpe4":"mozilla","cpe5":"firefox","cpe6":"*","cpe7":"*","cpe8":"*","cpe9":"*","cpe10":"*","cpe11":"*","cpe12":"*","cpe13":"*"},{"cve_year":"2021","cve_id":"29991","vulnerable":"1","versionEndIncluding":"","cpe1":"cpe","cpe2":"2.3","cpe3":"a","cpe4":"mozilla","cpe5":"thunderbird","cpe6":"*","cpe7":"*","cpe8":"*","cpe9":"*","cpe10":"*","cpe11":"*","cpe12":"*","cpe13":"*"}],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[{"cve":"CVE-2021-29991","qid":"198470","title":"Ubuntu Security Notification for Firefox Vulnerability (USN-5047-1)"},{"cve":"CVE-2021-29991","qid":"198641","title":"Ubuntu Security Notification for Thunderbird Vulnerabilities (USN-5248-1)"},{"cve":"CVE-2021-29991","qid":"296066","title":"Oracle Solaris 11.4 Support Repository Update (SRU) 40.107.3 Missing (CPUOCT2021)"},{"cve":"CVE-2021-29991","qid":"375824","title":"Mozilla Firefox Header Splitting Vulnerability(MFSA2021-37)"},{"cve":"CVE-2021-29991","qid":"375825","title":"Mozilla Thunderbird Header Splitting Vulnerability(MFSA2021-37)"},{"cve":"CVE-2021-29991","qid":"502080","title":"Alpine Linux Security Update for firefox"},{"cve":"CVE-2021-29991","qid":"502381","title":"Alpine Linux Security Update for thunderbird"},{"cve":"CVE-2021-29991","qid":"503632","title":"Alpine Linux Security Update for thunderbird"},{"cve":"CVE-2021-29991","qid":"503634","title":"Alpine Linux Security Update for thunderbird"},{"cve":"CVE-2021-29991","qid":"503650","title":"Alpine Linux Security Update for thunderbird"},{"cve":"CVE-2021-29991","qid":"503669","title":"Alpine Linux Security Update for thunderbird"},{"cve":"CVE-2021-29991","qid":"503851","title":"Alpine Linux Security Update for firefox"},{"cve":"CVE-2021-29991","qid":"506260","title":"Alpine Linux Security Update for thunderbird"},{"cve":"CVE-2021-29991","qid":"751210","title":"SUSE Enterprise Linux Security Update for MozillaFirefox (SUSE-SU-2021:3331-1)"},{"cve":"CVE-2021-29991","qid":"751226","title":"OpenSUSE Security Update for MozillaFirefox (openSUSE-SU-2021:3331-1)"},{"cve":"CVE-2021-29991","qid":"751237","title":"OpenSUSE Security Update for MozillaFirefox (openSUSE-SU-2021:3451-1)"},{"cve":"CVE-2021-29991","qid":"751246","title":"OpenSUSE Security Update for MozillaFirefox (openSUSE-SU-2021:1367-1)"},{"cve":"CVE-2021-29991","qid":"751369","title":"SUSE Enterprise Linux Security Update for MozillaFirefox (SUSE-SU-2021:3191-1)"},{"cve":"CVE-2021-29991","qid":"751542","title":"OpenSUSE Security Update for MozillaThunderbird (openSUSE-SU-2021:4150-1)"},{"cve":"CVE-2021-29991","qid":"751566","title":"OpenSUSE Security Update for MozillaThunderbird (openSUSE-SU-2021:1635-1)"},{"cve":"CVE-2021-29991","qid":"752111","title":"SUSE Enterprise Linux Security Update for MozillaFirefox (SUSE-SU-2022:1582-1)"},{"cve":"CVE-2021-29991","qid":"752113","title":"SUSE Enterprise Linux Security Update for MozillaFirefox (SUSE-SU-2022:1577-1)"}]},"source_records":{"cve_program":{"data_type":"CVE","data_format":"MITRE","data_version":"4.0","CVE_data_meta":{"ID":"CVE-2021-29991","ASSIGNER":"security@mozilla.org","STATE":"PUBLIC"},"affects":{"vendor":{"vendor_data":[{"vendor_name":"Mozilla","product":{"product_data":[{"product_name":"Firefox","version":{"version_data":[{"version_value":"91.0.1","version_affected":"<"}]}},{"product_name":"Thunderbird","version":{"version_data":[{"version_value":"91.0.1","version_affected":"<"}]}}]}}]}},"problemtype":{"problemtype_data":[{"description":[{"lang":"eng","value":"Header Splitting possible with HTTP/3 Responses"}]}]},"references":{"reference_data":[{"url":"https://www.mozilla.org/security/advisories/mfsa2021-37/","refsource":"MISC","name":"https://www.mozilla.org/security/advisories/mfsa2021-37/"},{"url":"https://bugzilla.mozilla.org/show_bug.cgi?id=1724896","refsource":"MISC","name":"https://bugzilla.mozilla.org/show_bug.cgi?id=1724896"}]},"description":{"description_data":[{"lang":"eng","value":"Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two separate headers. This allowed for a header splitting attack against servers using HTTP/3. This vulnerability affects Firefox < 91.0.1 and Thunderbird < 91.0.1."}]}},"nvd":{"publishedDate":"2021-11-03 01:15:00","lastModifiedDate":"2021-11-04 21:01:00","problem_types":["CWE-444"],"metrics":{"baseMetricV3":{"cvssV3":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"REQUIRED","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"NONE","baseScore":8.1,"baseSeverity":"HIGH"},"exploitabilityScore":2.8,"impactScore":5.2},"baseMetricV2":{"cvssV2":{"version":"2.0","vectorString":"AV:N/AC:M/Au:N/C:P/I:P/A:N","accessVector":"NETWORK","accessComplexity":"MEDIUM","authentication":"NONE","confidentialityImpact":"PARTIAL","integrityImpact":"PARTIAL","availabilityImpact":"NONE","baseScore":5.8},"severity":"MEDIUM","exploitabilityScore":8.6,"impactScore":4.9,"acInsufInfo":false,"obtainAllPrivilege":false,"obtainUserPrivilege":false,"obtainOtherPrivilege":false,"userInteractionRequired":true}},"configurations":{"CVE_data_version":"4.0","nodes":[{"operator":"OR","children":[],"cpe_match":[{"vulnerable":true,"cpe23Uri":"cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*","versionEndExcluding":"91.0.1","cpe_name":[]},{"vulnerable":true,"cpe23Uri":"cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*","versionEndExcluding":"91.0.1","cpe_name":[]}]}]}},"legacy_mitre":{"record":{"CveYear":"2021","CveId":"29991","Ordinal":"205222","Title":"CVE-2021-29991","CVE":"CVE-2021-29991","Year":"2021"},"notes":[{"CveYear":"2021","CveId":"29991","Ordinal":"1","NoteData":"Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two separate headers. This allowed for a header splitting attack against servers using HTTP/3. This vulnerability affects Firefox < 91.0.1 and Thunderbird < 91.0.1.","Type":"Description","Title":null},{"CveYear":"2021","CveId":"29991","Ordinal":"2","NoteData":"2021-11-02","Type":"Other","Title":"Published"},{"CveYear":"2021","CveId":"29991","Ordinal":"3","NoteData":"2021-11-02","Type":"Other","Title":"Modified"}]}}}