CVE-2026-92239: A maliciously constructed IMAP line could cause an out-of-bounds buffer read

Routine

HIGH 8.1UPGRADE

CVE-2026-92239 is a high-severity flaw (CVSS 8.1) affecting thunderbird. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A maliciously constructed IMAP line could cause an out-of-bounds buffer read. This vulnerability was fixed in Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3.

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.4% (top 65%)
CISA exploited list	No
Weakness	CWE-125
Published	2026-09-15
Last modified	2026-09-24

Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Last updated 2026-09-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-15 20:19 UTCPublished CVE record published
2026-09-24 14:15 UTCUpdated Record last modified

mozilla thunderbird UPGRADE

Affected: < 140.16.0 · >= 141.0 and < 153.3.0 · >= 154.0 and < 156.0

Fixed in: 140.16.0, 153.3.0, 156.0

Safe to downgrade to: a release before 141.0

1. Check installed version

apt-cache policy thunderbird || rpm -q thunderbird || thunderbird --version

2. UPGRADE to 140.16.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade thunderbird

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade thunderbird

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 141.0 (Debian / Ubuntu)

apt-cache madison thunderbird sudo apt install thunderbird=<VERSION_BEFORE_141.0> sudo apt-mark hold thunderbird

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list thunderbird sudo dnf downgrade thunderbird-<VERSION_BEFORE_141.0> sudo dnf versionlock add thunderbird

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-92239?

thunderbird: upgrade to 140.16.0, 153.3.0, 156.0. Exact commands for each OS are on this page.

Is CVE-2026-92239 being exploited?

CVE-2026-92239 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-92239 affect?

CVE-2026-92239 affects thunderbird. Severity is high (CVSS 8.1). A maliciously constructed IMAP line could cause an out-of-bounds buffer read. This vulnerability was fixed in Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3.

How urgent is CVE-2026-92239?

Priority 37/100. High severity

Software pages

Mozilla Thunderbird vulnerabilities

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References

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