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CVE-2021-29969

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected...

5.9 MediumFix available

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

1.20%Up 0.6 points since Aug 6, 2021
90%50%10%1%

What each source reports

NVD Score used 5.9

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Record
CVE-2021-29969
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS 2.0
4.3 MediumAV:N/AC:M/Au:N/C:P/I:N/A:N
Weakness
CWE-552
Updated
2026-11-02
CVE List No score

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Record
CVE-2021-29969
Updated
2026-11-02
EUVDEUVD-2021-16428 No score

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Record
EUVD-2021-16428
Updated
2026-11-03
GitHub AdvisoriesGHSA-ggp3-c9px-5c4p 5.9

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected...

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Record
GHSA-ggp3-c9px-5c4p
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-552
Updated
2026-11-02
OSVALPINE-CVE-2021-29969 5.9

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Record
ALPINE-CVE-2021-29969
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-03
OSV 5.9

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Record
CVE-2021-29969
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
Show 13 moreShow less
OSVDEBIAN-CVE-2021-29969 5.9

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Record
DEBIAN-CVE-2021-29969
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVRHSA-2021:2881 8.8

Red Hat Security Advisory: thunderbird security update

Record
RHSA-2021:2881
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVRHSA-2021:2882 8.8

Red Hat Security Advisory: thunderbird security update

Record
RHSA-2021:2882
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVRHSA-2021:2883 8.8

Red Hat Security Advisory: thunderbird security update

Record
RHSA-2021:2883
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVRHSA-2021:2914 8.8

Red Hat Security Advisory: thunderbird security update

Record
RHSA-2021:2914
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVRLSA-2021:2883 8.8

Important: thunderbird security update

Mozilla Thunderbird is a standalone mail and newsgroup client.

This update upgrades Thunderbird to version 78.12.0.

Security Fix(es):

  • Mozilla: IMAP server responses sent by a MITM prior to STARTTLS could be processed (CVE-2021-29969)

  • Mozilla: Use-after-free in accessibility features of a document (CVE-2021-29970)

  • Mozilla: Memory safety bugs fixed in Firefox 90 and Firefox ESR 78.12 (CVE-2021-29976)

  • chromium-browser: Out of bounds write in ANGLE (CVE-2021-30547)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Record
RLSA-2021:2883
CVSS 3.1
8.8 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2021-29969 5.9

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

Record
UBUNTU-CVE-2021-29969
CVSS 3.1
5.9 MediumCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVMGASA-2021-0355 No score

Updated thunderbird packages fix security vulnerabilities

IMAP server responses sent by a MITM prior to STARTTLS could be processed (CVE-2021-29969).

Use-after-free in accessibility features of a document (CVE-2021-29970).

Out of bounds write in ANGLE (CVE-2021-30547).

Memory safety bugs fixed in Thunderbird 78.12 (CVE-2021-29976).

Record
MGASA-2021-0355
Updated
2026-11-02
OSVopenSUSE-SU-2021:1091-1 No score

Security update for MozillaThunderbird

This update for MozillaThunderbird fixes the following issues:

Mozilla Thunderbird 78.12

  • fixed: Sending an email containing HTML links with spaces in the URL sometimes resulted in broken links
  • fixed: Folder Pane display theme fixes for macOS
  • fixed: Chat account settings did not always save as expected
  • fixed: RSS feed subscriptions sometimes lost
  • fixed: Calendar: A parsing error for alarm triggers of type 'DURATION' caused sync problems for some users
  • fixed: Various security fixes

MFSA 2021-30 (bsc#1188275)

  • CVE-2021-29969: IMAP server responses sent by a MITM prior to STARTTLS could be processed
  • CVE-2021-29970: Use-after-free in accessibility features of a document
  • CVE-2021-30547: Out of bounds write in ANGLE
  • CVE-2021-29976: Memory safety bugs fixed in Thunderbird 78.12

This update was imported from the SUSE:SLE-15-SP2:Update update project.

Record
openSUSE-SU-2021:1091-1
Updated
2026-11-02
OSVopenSUSE-SU-2021:2458-1 No score

Security update for MozillaThunderbird

This update for MozillaThunderbird fixes the following issues:

Mozilla Thunderbird 78.12

  • fixed: Sending an email containing HTML links with spaces in the URL sometimes resulted in broken links
  • fixed: Folder Pane display theme fixes for macOS
  • fixed: Chat account settings did not always save as expected
  • fixed: RSS feed subscriptions sometimes lost
  • fixed: Calendar: A parsing error for alarm triggers of type 'DURATION' caused sync problems for some users
  • fixed: Various security fixes

MFSA 2021-30 (bsc#1188275)

  • CVE-2021-29969: IMAP server responses sent by a MITM prior to STARTTLS could be processed
  • CVE-2021-29970: Use-after-free in accessibility features of a document
  • CVE-2021-30547: Out of bounds write in ANGLE
  • CVE-2021-29976: Memory safety bugs fixed in Thunderbird 78.12
Record
openSUSE-SU-2021:2458-1
Updated
2026-11-02
OSVopenSUSE-SU-2024:10601-1 No score

MozillaThunderbird-91.1.1-1.1 on GA media

These are all security issues fixed in the MozillaThunderbird-91.1.1-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:10601-1
Updated
2026-11-02
OSVSUSE-SU-2021:2458-1 No score

Security update for MozillaThunderbird

This update for MozillaThunderbird fixes the following issues:

Mozilla Thunderbird 78.12

  • fixed: Sending an email containing HTML links with spaces in the URL sometimes resulted in broken links
  • fixed: Folder Pane display theme fixes for macOS
  • fixed: Chat account settings did not always save as expected
  • fixed: RSS feed subscriptions sometimes lost
  • fixed: Calendar: A parsing error for alarm triggers of type 'DURATION' caused sync problems for some users
  • fixed: Various security fixes

MFSA 2021-30 (bsc#1188275)

  • CVE-2021-29969: IMAP server responses sent by a MITM prior to STARTTLS could be processed
  • CVE-2021-29970: Use-after-free in accessibility features of a document
  • CVE-2021-30547: Out of bounds write in ANGLE
  • CVE-2021-29976: Memory safety bugs fixed in Thunderbird 78.12
Record
SUSE-SU-2021:2458-1
Updated
2026-11-02
OSVUSN-5058-1 No score

thunderbird vulnerabilities

It was discovered that Thunderbird didn't ignore IMAP server responses prior to completion of the STARTTLS handshake. A person-in-the-middle could potentially exploit this to trick Thunderbird into showing incorrect information. (CVE-2021-29969)

Multiple security issues were discovered in Thunderbird. If a user were tricked into opening a specially crafted website in a browsing context, an attacker could potentially exploit these to cause a denial of service, or execute arbitrary code. (CVE-2021-29970, CVE-2021-29976, CVE-2021-29980, CVE-2021-29984, CVE-2021-29985, CVE-2021-29986, CVE-2021-29988, CVE-2021-29989, CVE-2021-30547)

Record
USN-5058-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
thunderbird
Alpine:v3.16
 before 91.3.2-r0
91.3.2-r0
thunderbird
Alpine:v3.17
 before 91.3.2-r0
91.3.2-r0
thunderbird
Alpine:v3.18
 before 91.3.2-r0
91.3.2-r0
thunderbird
Alpine:v3.19
 before 91.3.2-r0
91.3.2-r0
thunderbird
Alpine:v3.20
 before 91.3.2-r0
91.3.2-r0
thunderbird
Alpine:v3.21
 before 91.3.2-r0
91.3.2-r0
thunderbird
Alpine:v3.22
 before 91.3.2-r0
91.3.2-r0
thunderbird
Alpine:v3.23
 before 91.3.2-r0
91.3.2-r0
thunderbird
Debian:12
 before 1:78.12.0-1
1:78.12.0-1
thunderbird
Debian:13
 before 1:78.12.0-1
1:78.12.0-1
Show 28 moreShow less
Affected packages
PackageAffectedFixed
thunderbird
Debian:14
 before 1:78.12.0-1
1:78.12.0-1
thunderbird
Debian:9
 before 1:78.12.0-1~deb9u1, plus listed versions
1.5-41.5.0.2-11.5.0.2-21.5.0.2-31.5.0.4-1
Show 45 moreShow less
1.5.0.4-21.5.0.4-31.5.0.5-11.5.0.7-11.5.0.7-21:52.4.0-11:52.4.0-1~deb7u11:52.4.0-1~deb8u11:52.4.0-1~deb9u11:52.4.0-2~exp11:52.5.0-11:52.5.0-1~deb7u11:52.5.0-1~deb8u11:52.5.0-1~deb9u11:52.5.2-11:52.5.2-1~deb7u11:52.5.2-21:52.5.2-2~deb8u11:52.5.2-2~deb9u11:52.6.0-11:52.6.0-1+alpha.11:52.6.0-1+alpha.21:52.6.0-1~deb7u11:52.6.0-1~deb8u11:52.6.0-1~deb9u11:52.7.0-11:52.7.0-1~deb7u11:52.7.0-1~deb8u11:52.7.0-1~deb9u11:52.8.0-11:52.8.0-1~deb7u11:52.8.0-1~deb8u11:52.8.0-1~deb9u11:52.9.0-11:52.9.1-11:52.9.1-1~deb8u11:52.9.1-1~deb9u11:58.0~b3-11:60.0-11:60.0-21:60.0-2~deb9u11:60.0-31:60.0-3~deb9u11:60.0~b10-11:60.0~b2-1
1:78.12.0-1~deb9u1
thunderbird
Debian:10
 before 1:78.12.0-1~deb10u1, plus listed versions
1:60.7.2-11:60.8.0-11:60.8.0-1~deb10u11:60.8.0-1~deb8u11:60.8.0-1~deb9u1
Show 45 moreShow less
1:60.8.0-21:60.9.0-11:60.9.0-1~deb10u11:60.9.0-1~deb8u11:60.9.0-1~deb9u11:65.0~b1-11:66.0~b1-11:67.0~b3-11:68.0~b1-11:68.1.1-1~exp11:68.1.2-1~exp11:68.10.0-11:68.10.0-1~deb10u11:68.10.0-1~deb9u11:68.11.0-11:68.11.0-1~deb10u11:68.11.0-1~deb9u11:68.11.0-21:68.11.0-31:68.12.0-11:68.12.0-1~deb10u11:68.12.0-1~deb9u11:68.12.0-1~deb9u21:68.2.1-11:68.2.2-11:68.2.2-1~deb10u11:68.2.2-1~deb8u11:68.2.2-1~deb9u11:68.3.0-11:68.3.0-21:68.3.0-2~deb10u11:68.3.0-2~deb8u11:68.3.0-2~deb9u11:68.3.1-11:68.4.1-11:68.4.1-1~deb10u11:68.4.1-1~deb8u11:68.4.1-1~deb9u11:68.4.2-11:68.5.0-11:68.5.0-1~deb10u11:68.5.0-1~deb8u11:68.5.0-1~deb9u11:68.6.0-11:68.6.0-1~deb10u1
1:78.12.0-1~deb10u1
thunderbird
Mageia:8
 before 78.12.0-1.mga8
78.12.0-1.mga8
thunderbird-l10n
Mageia:8
 before 78.12.0-1.mga8
78.12.0-1.mga8
thunderbird
Red Hat:enterprise_linux:7::client
 before 0:78.12.0-2.el7_9
0:78.12.0-2.el7_9
thunderbird-debuginfo
Red Hat:enterprise_linux:7::client
 before 0:78.12.0-2.el7_9
0:78.12.0-2.el7_9
thunderbird
Red Hat:enterprise_linux:7::server
 before 0:78.12.0-2.el7_9
0:78.12.0-2.el7_9
thunderbird-debuginfo
Red Hat:enterprise_linux:7::server
 before 0:78.12.0-2.el7_9
0:78.12.0-2.el7_9
thunderbird
Red Hat:enterprise_linux:7::workstation
 before 0:78.12.0-2.el7_9
0:78.12.0-2.el7_9
thunderbird-debuginfo
Red Hat:enterprise_linux:7::workstation
 before 0:78.12.0-2.el7_9
0:78.12.0-2.el7_9
thunderbird
Red Hat:rhel_eus:8.1::appstream
 before 0:78.12.0-2.el8_1
0:78.12.0-2.el8_1
thunderbird-debuginfo
Red Hat:rhel_eus:8.1::appstream
 before 0:78.12.0-2.el8_1
0:78.12.0-2.el8_1
thunderbird-debugsource
Red Hat:rhel_eus:8.1::appstream
 before 0:78.12.0-2.el8_1
0:78.12.0-2.el8_1
thunderbird
Red Hat:enterprise_linux:8::appstream
 before 0:78.12.0-3.el8_4
0:78.12.0-3.el8_4
thunderbird-debuginfo
Red Hat:enterprise_linux:8::appstream
 before 0:78.12.0-3.el8_4
0:78.12.0-3.el8_4
thunderbird-debugsource
Red Hat:enterprise_linux:8::appstream
 before 0:78.12.0-3.el8_4
0:78.12.0-3.el8_4
thunderbird
Red Hat:rhel_eus:8.2::appstream
 before 0:78.12.0-2.el8_2
0:78.12.0-2.el8_2
thunderbird-debuginfo
Red Hat:rhel_eus:8.2::appstream
 before 0:78.12.0-2.el8_2
0:78.12.0-2.el8_2
thunderbird-debugsource
Red Hat:rhel_eus:8.2::appstream
 before 0:78.12.0-2.el8_2
0:78.12.0-2.el8_2
thunderbird
Rocky Linux:8
 before 0:78.12.0-3.el8_4
0:78.12.0-3.el8_4
MozillaThunderbird
SUSE:Linux Enterprise Workstation Extension 15 SP2
 before 78.12.0-8.33.1
78.12.0-8.33.1
MozillaThunderbird
SUSE:Linux Enterprise Workstation Extension 15 SP3
 before 78.12.0-8.33.1
78.12.0-8.33.1
thunderbird
Ubuntu:18.04:LTS
 before 1:78.13.0+build1-0ubuntu0.18.04.1, plus listed versions
1:52.4.0+build1-0ubuntu21:52.6.0+build1-0ubuntu11:52.7.0+build1-0ubuntu11:52.8.0+build1-0ubuntu0.18.04.11:52.9.1+build3-0ubuntu0.18.04.1
Show 17 moreShow less
1:60.2.1+build1-0ubuntu0.18.04.21:60.4.0+build2-0ubuntu0.18.04.11:60.5.1+build2-0ubuntu0.18.04.11:60.6.1+build2-0ubuntu0.18.04.11:60.7.0+build1-0ubuntu0.18.04.11:60.7.1+build1-0ubuntu0.18.04.11:60.7.2+build2-0ubuntu0.18.04.11:60.8.0+build1-0ubuntu0.18.04.11:60.9.0+build1-0ubuntu0.18.04.11:68.2.1+build1-0ubuntu0.18.04.11:68.2.2+build1-0ubuntu0.18.04.11:68.4.1+build1-0ubuntu0.18.04.11:68.7.0+build1-0ubuntu0.18.04.11:68.8.0+build2-0ubuntu0.18.04.21:68.10.0+build1-0ubuntu0.18.04.11:78.8.1+build1-0ubuntu0.18.04.11:78.11.0+build1-0ubuntu0.18.04.2
1:78.13.0+build1-0ubuntu0.18.04.1
thunderbird
Ubuntu:20.04:LTS
 before 1:78.13.0+build1-0ubuntu0.20.04.2, plus listed versions
1:68.1.2+build1-0ubuntu11:68.1.2+build1-0ubuntu21:68.2.1+build1-0ubuntu11:68.2.2+build1-0ubuntu11:68.3.0+build2-0ubuntu1
Show 12 moreShow less
1:68.3.1+build1-0ubuntu21:68.4.1+build1-0ubuntu11:68.4.2+build2-0ubuntu11:68.5.0+build1-0ubuntu11:68.6.0+build2-0ubuntu11:68.7.0+build1-0ubuntu11:68.7.0+build1-0ubuntu21:68.8.0+build2-0ubuntu0.20.04.21:68.10.0+build1-0ubuntu0.20.04.11:78.7.1+build1-0ubuntu0.20.04.11:78.8.1+build1-0ubuntu0.20.04.11:78.11.0+build1-0ubuntu0.20.04.2
1:78.13.0+build1-0ubuntu0.20.04.2
MozillaThunderbird
openSUSE:Leap 15.2
 before 78.12.0-lp152.2.48.2
78.12.0-lp152.2.48.2
MozillaThunderbird
openSUSE:Leap 15.3
 before 78.12.0-8.33.1
78.12.0-8.33.1
MozillaThunderbird
openSUSE:Tumbleweed
 before 91.1.1-1.1
91.1.1-1.1

History

History
RecordedChangedSources
affected, aliases, referencesOSV
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-29969 is a medium vulnerability (CVSS 5.9) in Mozilla Thunderbird, published July 16, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.20%, the 68th percentile. Fixed in thunderbird 91.3.2-r0.

References

Show 194 moreShow less
This page doesn't list everything

Left out here: 227 versions and 245 references. The JSON record has them.

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