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Vulnerability details: VCID-wyyg-6msu-nuhn
Vulnerability ID VCID-wyyg-6msu-nuhn
Aliases CVE-2021-4126
Summary 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.
Status Published
Exploitability 0.5
Weighted Severity 5.9
Risk 3.0
Affected and Fixed Packages Package Details
Weaknesses (0)
There are no known CWE.
System Score Found at
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
epss 0.00125 https://api.first.org/data/v1/epss?cve=CVE-2021-4126
cvssv3.1 6.5 https://bugzilla.mozilla.org/show_bug.cgi?id=1732310
ssvc Track https://bugzilla.mozilla.org/show_bug.cgi?id=1732310
cvssv3.1 5.3 https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
cvssv3.1 6.5 https://nvd.nist.gov/vuln/detail/CVE-2021-4126
generic_textual none https://www.mozilla.org/en-US/security/advisories/mfsa2021-55
cvssv3.1 6.5 https://www.mozilla.org/security/advisories/mfsa2021-55/
ssvc Track https://www.mozilla.org/security/advisories/mfsa2021-55/
Reference id Reference type URL
https://api.first.org/data/v1/epss?cve=CVE-2021-4126
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38496
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38500
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38502
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38503
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38504
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38506
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38507
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38508
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38509
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-4126
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-4129
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43528
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43529
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43534
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43535
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43536
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43537
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43538
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43539
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43541
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43542
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43543
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43545
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43546
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-44538
https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
CVE-2021-4126 https://nvd.nist.gov/vuln/detail/CVE-2021-4126
mfsa2021-55 https://www.mozilla.org/en-US/security/advisories/mfsa2021-55
mfsa2021-55 https://www.mozilla.org/security/advisories/mfsa2021-55/
show_bug.cgi?id=1732310 https://bugzilla.mozilla.org/show_bug.cgi?id=1732310
USN-5246-1 https://usn.ubuntu.com/5246-1/
USN-5248-1 https://usn.ubuntu.com/5248-1/
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N Found at https://bugzilla.mozilla.org/show_bug.cgi?id=1732310
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:N/T:P/P:M/B:A/M:M/D:T/2025-04-16T15:36:07Z/ Found at https://bugzilla.mozilla.org/show_bug.cgi?id=1732310
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N Found at https://ftp.suse.com/pub/projects/security/yaml/suse-cvss-scores.yaml
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N Found at https://nvd.nist.gov/vuln/detail/CVE-2021-4126
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N Found at https://www.mozilla.org/security/advisories/mfsa2021-55/
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: SSVCv2/E:N/A:N/T:P/P:M/B:A/M:M/D:T/2025-04-16T15:36:07Z/ Found at https://www.mozilla.org/security/advisories/mfsa2021-55/
Exploit Prediction Scoring System (EPSS)
Percentile 0.32615
EPSS Score 0.00125
Published At July 30, 2025, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2025-07-31T08:09:47.460933+00:00 Mozilla Importer Import https://github.com/mozilla/foundation-security-advisories/blob/master/announce/2021/mfsa2021-55.yml 37.0.0