CVE-2026-16389: Incorrect boundary conditions, integer overflow in the Libraries component in NSS

Q: How do I fix CVE-2026-16389?

firefox: upgrade to 153.0.0; thunderbird: upgrade to 153.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-16389 being exploited?

CVE-2026-16389 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-16389 affect?

CVE-2026-16389 affects firefox, thunderbird. Severity is critical (CVSS 9.8). Incorrect boundary conditions, integer overflow in the Libraries component in NSS. This vulnerability was fixed in Firefox 153 and Thunderbird 153.

Q: How urgent is CVE-2026-16389?

Priority 54/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

This month

CRITICAL 9.8REMOTEUPGRADEUPGRADE

CVE-2026-16389 is a critical-severity flaw (CVSS 9.8) affecting firefox, thunderbird. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Incorrect boundary conditions, integer overflow in the Libraries component in NSS. This vulnerability was fixed in Firefox 153 and Thunderbird 153.

Why this priority

Critical severity
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 54%)
CISA exploited list	No
Weakness	CWE-190
Published	2026-07-21
Last modified	2026-10-24

Publisher (CNA): Mozilla Corporation · Vendor: mozilla

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-21 13:17 UTCPublished CVE record published
2026-10-24 20:10 UTCUpdated Record last modified

mozilla firefox UPGRADE

Affected: < 153.0.0

Fixed in: 153.0.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 153.0.0 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade firefox

Note

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

mozilla thunderbird UPGRADE

Affected: < 153.0

Fixed in: 153.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 153.0 (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.

Exact fixes by distribution

Fedora 46 · conda · FIXED · 26.9.4-2.fc46 · FEDORA-2026-09931756f1 · source

sudo dnf upgrade --advisory=FEDORA-2026-09931756f1

Ubuntu 22.04 · firefox · NOT AFFECTED

Ubuntu 24.04 · firefox · NOT AFFECTED

Ubuntu 22.04 · thunderbird · NO FIX YET

Ubuntu 24.04 · thunderbird · NOT AFFECTED

Debian 12 · nss · FIXED · 2:3.87.1-1+deb12u4

sudo apt update && sudo apt install --only-upgrade nss dpkg --compare-versions "$(dpkg-query -W -f='${Version}' nss)" ge "2:3.87.1-1+deb12u4" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · nss · FIXED · 2:3.110-1+deb13u4

sudo apt update && sudo apt install --only-upgrade nss dpkg --compare-versions "$(dpkg-query -W -f='${Version}' nss)" ge "2:3.110-1+deb13u4" && echo PATCHED || echo STILL-VULNERABLE

RHEL 10 · firefox · NOT AFFECTED

RHEL 10 · rhel10/firefox-flatpak · NOT AFFECTED

RHEL 10 · rhel10/thunderbird-flatpak · NOT AFFECTED

RHEL 10 · thunderbird · NOT AFFECTED

RHEL 6 · firefox · NOT AFFECTED

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: bugzilla.mozilla.org/show_bug.cgi?id=2043887

Advisories and coverage

Official advisories

Amazon Linux 2023 ALAS: ALAS2023-2026-3242 (medium): nss 2026-10-24

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-2026-16389?

firefox: upgrade to 153.0.0; thunderbird: upgrade to 153.0. Exact commands for each OS are on this page.

Is CVE-2026-16389 being exploited?

CVE-2026-16389 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-2026-16389 affect?

CVE-2026-16389 affects firefox, thunderbird. Severity is critical (CVSS 9.8). Incorrect boundary conditions, integer overflow in the Libraries component in NSS. This vulnerability was fixed in Firefox 153 and Thunderbird 153.

How urgent is CVE-2026-16389?

Priority 54/100. Critical severity; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Software pages

Mozilla Firefox vulnerabilities · Mozilla Thunderbird vulnerabilities

Related CVEs

CVE-2026-16353 CRITICAL 9.8 UPGRADE UPGRADE Invalid pointer in the DOM: Bindings (WebIDL) component
CVE-2026-16360 CRITICAL 9.8 UPGRADE UPGRADE Memory safety bugs present in Thunderbird ESR 140.12 and Thunderbird 152
CVE-2026-16363 CRITICAL 9.8 UPGRADE UPGRADE JIT miscompilation in the JavaScript: WebAssembly component
CVE-2026-16369 CRITICAL 9.8 UPGRADE UPGRADE Integer overflow in the JavaScript: WebAssembly component
CVE-2026-16408 CRITICAL 9.8 UPGRADE Integer overflow in the Audio/Video: Playback component

References

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