No exploitation reportedFix available

CVE-2020-26970

Q: Is CVE-2020-26970 actively exploited?

Active exploitation of CVE-2020-26970 has not been confirmed. Its EPSS score was 1.2% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2020-26970?

CVE-2020-26970 has a CVSS v3 base score of 8.8 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

No exploitation reported by the sources we read.

Published2020-12-09
Fixed in78.5.1
WeaknessCWE-787

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC

2020-12-0901:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2020-26970?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2020-26970?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Mozilla thunderbird

Branch	Affected	Fixed in	Source
78.5	< 78.5.1	78.5.1	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Mozilla thunderbird to 78.5.1

Advisories and patches

bugzilla.mozilla.orgVendor Advisory
www.mozilla.orgVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.18.8read 2026-10-23
NVDCVSS 2.09.3read 2026-10-23
NVDweakness (CWE)CWE-787read 2026-10-23
FIRST EPSSEPSS score1.2 %2026-10-23

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Published: 2020-12-09
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2020-26970?

Is CVE-2020-26970 actively exploited?

Active exploitation of CVE-2020-26970 has not been confirmed. Its EPSS score was 1.2% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2020-26970?

CVE-2020-26970 has a CVSS v3 base score of 8.8 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

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