{"answers":{"affected":"It affects 1 product.","exploited":"There is no known exploitation of CVE-2021-4126 in the wild and no public exploit code.","fix":"Upgrade to a fixed version.","what":"CVE-2021-4126 is a medium-severity vulnerability in Mozilla Thunderbird, published on 22 Dec 2022. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link."},"fix_prompt":"Check this codebase for CVE-2021-4126 and fix it if it is affected.\n\nWhat it is: CVE-2021-4126 is a medium-severity vulnerability in Mozilla Thunderbird, published on 22 Dec 2022. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.\nExploitation: There is no known exploitation of CVE-2021-4126 in the wild and no public exploit code.\n\nAffected product: Mozilla Thunderbird. No package-level version data is available, so check the vendor advisory linked from the reference page.\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2021-4126/ (Markdown: https://insights.sbomify.com/CVE-2021-4126/index.md)","id":"CVE-2021-4126","markdown":"https://insights.sbomify.com/CVE-2021-4126/index.md","name":"CVE-2021-4126","record":{"aliases":["DEBIAN-CVE-2021-4126","GHSA-v2cr-gvw4-g56p","UBUNTU-CVE-2021-4126"],"analysis":{"component_type":"desktop_application","fix_type":"upgrade","impacts":["security_bypass"],"network_reachable":"yes","non_default_config":false,"product_category":"Thunderbird email client","requires_auth":"none","summary":"Thunderbird incorrectly validates signatures on nested MIME messages, allowing attackers to spoof signed content and bypass security checks.","user_interaction":"required","vuln_class":"security_feature_bypass"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"mozilla","cpe":[{"product":"thunderbird","vendor":"mozilla"}],"cvss":{"score":6.5,"severity":"medium","source":"cisa-adp","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N","version":"3.1"},"cwes":[],"description":"When receiving an OpenPGP/MIME signed email message that contains an additional outer MIME message layer, for example a message footer added by a mailing list gateway, Thunderbird only considered the inner signed message for the signature validity. This gave the false impression that the additional contents were also covered by the digital signature. Starting with Thunderbird version 91.4.1, only the signature that belongs to the top level MIME part will be considered for the displayed status. This vulnerability affects Thunderbird \u003c 91.4.1.","ecosystems":[],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"Security feature bypass in Thunderbird","id":"CVE-2021-4126","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":"mozilla:thunderbird","products":["mozilla:thunderbird"],"type":"security_feature_bypass","year":"2021"},"n_packages":0,"n_references":2,"next":{"headline":"Other in Firefox ESR","id":"CVE-2021-4127"},"packages":[],"prev":{"headline":"Deserialization in kube-reporting/hive","id":"CVE-2021-4125"},"products":["Thunderbird"],"published":"2022-12-22","related":[{"cvss_score":9.8,"headline":"Ambiguous parsing of mail headers","id":"CVE-2026-92238","kev_date_added":null,"published":"2026-09-15"},{"cvss_score":9.8,"headline":"Calendar invitation attachments could launch local executables","id":"CVE-2026-84637","kev_date_added":null,"published":"2026-09-01"},{"cvss_score":9.8,"headline":"Memory corruption in Thunderbird","id":"CVE-2021-43529","kev_date_added":null,"published":"2023-02-16"},{"cvss_score":9.8,"headline":"Memory corruption in Thunderbird","id":"CVE-2019-11703","kev_date_added":null,"published":"2019-07-23"},{"cvss_score":9.8,"headline":"Memory corruption in Thunderbird","id":"CVE-2019-11704","kev_date_added":null,"published":"2019-07-23"},{"cvss_score":9.8,"headline":"Memory corruption in Thunderbird","id":"CVE-2019-11705","kev_date_added":null,"published":"2019-07-23"},{"cvss_score":9.8,"headline":"Use after free in Thunderbird","id":"CVE-2018-18512","kev_date_added":null,"published":"2019-04-26"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"no","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2025-04-16","vendors":["Mozilla"]},"summary":"Thunderbird incorrectly validates signatures on nested MIME messages, allowing attackers to spoof signed content and bypass security checks.","url":"https://insights.sbomify.com/CVE-2021-4126/"}