Skip to content
Fencer Vulns
high 8.8

CVE-2020-26970 json

When reading SMTP server status codes, Thunderbird writes an integer value to a position on the stack that is intended to contain just one…

published 2020-12-09 5 y ago modified 2026-06-17 4 mo ago also EUVD-2020-19494

cvss
8.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 69%
public exploits
0
none known

Summary

When reading SMTP server status codes, Thunderbird writes an integer value to a position on the stack that is intended to contain just one byte. Depending on processor architecture and stack layout, this leads to stack corruption that may be exploitable. This vulnerability affects Thunderbird < 78.5.1.

Patch / fix

  • mozilla thunderbird 78.5.1
  • thunderbird Debian 14, Debian 13, Debian 12 1:78.5.1-1

debian advisories DEBIAN-CVE-2020-26970

  • thunderbird Ubuntu 18.04 LTS 1:78.8.1+build1-0ubuntu0.18.04.1
  • thunderbird Ubuntu 20.04 LTS 1:78.7.1+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2020-26970

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • thunderbird RHEL 7 78.5.1-1.el7_9
  • thunderbird RHEL 8 78.5.1-1.el8_3
  • thunderbird RHEL 8.0 E4S 78.6.0-1.el8_0
  • thunderbird RHEL 8.1 EUS 78.6.0-1.el8_1
  • thunderbird RHEL 8.2 EUS 78.5.1-1.el8_2

red hat advisories RHSA-2020:5645RHSA-2020:5644RHSA-2020:5399RHSA-2020:5400RHSA-2020:5398

  • MozillaThunderbird SLE Workstation Extension 15 SP2 78.6.0-8.3.1
  • MozillaThunderbird SLE Workstation Extension 15 SP1 78.5.1-3.110.2

suse advisories SUSE-SU-2020:3935-1SUSE-SU-2020:3642-1

  • MozillaThunderbird openSUSE Tumbleweed 91.1.1-1.1

opensuse advisories openSUSE-SU-2024:10601-1

  • thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 78.5.1-r0

alpine advisories ALPINE-CVE-2020-26970

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • thunderbird Arch Linux 78.6.0-1

arch linux advisories AVG-1315

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-26970 updated cvss 8.8

Mozilla: Stack overflow due to incorrect parsing of SMTP server response codes

  • Red Hat Enterprise Linux 5 thunderbird Red Hat Enterprise Linux 6 thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) thunderbird 78.5.1-1.el8_3
    fixed: vendor fix RHSA-2020:5398
  • Red Hat Enterprise Linux AppStream E4S (v. 8.0) thunderbird 78.6.0-1.el8_0
    fixed: vendor fix RHSA-2020:5645
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) thunderbird 78.6.0-1.el8_1
    fixed: vendor fix RHSA-2020:5644
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird 78.5.1-1.el8_2
    fixed: vendor fix RHSA-2020:5399
  • Red Hat Enterprise Linux Client (v. 7) thunderbird 78.5.1-1.el7_9 Red Hat Enterprise Linux Server Optional (v. 7) thunderbird 78.5.1-1.el7_9 Red Hat Enterprise Linux Workstation (v. 7) thunderbird 78.5.1-1.el7_9
    fixed: vendor fix RHSA-2020:5400

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.25% chance of exploitation in the next 30 days, higher than 69% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD 2.0 9.3 AV:N/AC:M/Au:N/C:C/I:C/A:C

Affected products

  • Mozilla Thunderbird

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.