← Vulnerability feed

Vulnerability record · CVE-2026-5731 · published 7 April 2026

CVE-2026-5731: Mozilla firefox memory buffer overflow vulnerability

Mozilla · Firefox

Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

9.8 CVSS 3.1 Critical EPSS 0.61% · top 52.9% CWE-119 · Memory buffer overflowCWE-787 · Out-of-bounds write
9.8CVSS 3.1 base score
0.61%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
33References
15 Jul 2026Last modified by NVD

Description

Memory safety bugs present in Firefox ESR 115.34.0, Firefox ESR 140.9.0, Thunderbird ESR 140.9.0, Firefox 149.0.1 and Thunderbird 149.0.1. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 149.0.2, Firefox ESR 115.34.1, Firefox ESR 140.9.1, Thunderbird 149.0.2, and Thunderbird 140.9.1.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://bugzilla.mozilla.org/buglist.cgi?bug_id=2021894%2C2022225%2C2022252%2C2022294%2C2023007%2C2023130%2C2023191%2C20 Broken Link
https://www.mozilla.org/security/advisories/mfsa2026-25/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-26/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-27/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-28/ Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2026-29/ Vendor Advisory
https://access.redhat.com/errata/RHSA-2026:11805
https://access.redhat.com/errata/RHSA-2026:11813
https://access.redhat.com/errata/RHSA-2026:12264
https://access.redhat.com/errata/RHSA-2026:13342
https://access.redhat.com/errata/RHSA-2026:13412
https://access.redhat.com/errata/RHSA-2026:13533
https://access.redhat.com/errata/RHSA-2026:13582
https://access.redhat.com/errata/RHSA-2026:13583
https://access.redhat.com/errata/RHSA-2026:13596
https://access.redhat.com/errata/RHSA-2026:13600
https://access.redhat.com/errata/RHSA-2026:13665
https://access.redhat.com/errata/RHSA-2026:13682
https://access.redhat.com/errata/RHSA-2026:13683
https://access.redhat.com/errata/RHSA-2026:13922
https://access.redhat.com/errata/RHSA-2026:13977
https://access.redhat.com/errata/RHSA-2026:14223
https://access.redhat.com/errata/RHSA-2026:14303
https://access.redhat.com/errata/RHSA-2026:15889
https://access.redhat.com/errata/RHSA-2026:7671
https://access.redhat.com/errata/RHSA-2026:7672
https://access.redhat.com/errata/RHSA-2026:8052
https://access.redhat.com/errata/RHSA-2026:8459
https://access.redhat.com/errata/RHSA-2026:9345
https://access.redhat.com/errata/RHSA-2026:9638
https://access.redhat.com/security/cve/CVE-2026-5731
https://bugzilla.redhat.com/show_bug.cgi?id=2455901
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5731.json

Track CVE-2026-5731 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2019-11708Mozilla Firefox and Thunderbird sandbox escape via Prompt:Open IPC validation flawThe Prompt:Open IPC message between child and parent processes does not sufficiently vet its parameters, letting a compromised child process cause th…KEVEPSS 56%analysed9.8CVE-2024-9680Mozilla Firefox and Thunderbird use-after-free in Animation timelinesA use-after-free flaw in Animation timelines allows an attacker to execute code in the content process of Firefox and Thunderbird. Mozilla reports ex…KEVEPSS 23%analysed9.8CVE-2010-3765Mozilla Firefox, Thunderbird and SeaMonkey memory corruption via appendChildA memory corruption flaw in Mozilla Firefox, Thunderbird and SeaMonkey arises from incorrect index tracking in nsCSSFrameConstructor::ContentAppended…KEVEPSS 83%analysed9.6CVE-2022-26486Firefox WebGPU IPC use-after-free enables sandbox escapeAn unexpected message in the WebGPU IPC framework triggers a use-after-free in Mozilla Firefox, Firefox ESR, Firefox for Android, Thunderbird and Foc…KEVEPSS 2.3%analysed8.8CVE-2023-5217libvpx VP8 encoding heap buffer overflow exploited via crafted HTMLA heap buffer overflow in the VP8 encoder in libvpx affects Google Chrome before 117.0.5938.132 and libvpx 1.13.1, and is reachable through a crafted…KEVEPSS 49%analysed8.8CVE-2023-4863libwebp Heap Buffer Overflow via Crafted WebP ImageA heap buffer overflow in libwebp allows an out-of-bounds memory write when processing a crafted WebP image. It affects Google Chrome before 116.0.58…KEVEPSS 100%analysed8.8CVE-2022-26485Firefox XSLT parameter removal use-after-freeRemoving an XSLT parameter during processing in Mozilla Firefox could trigger a use-after-free condition. Mozilla reported attacks in the wild abusin…KEVEPSS 14%analysed8.8CVE-2019-17026Firefox and Thunderbird IonMonkey JIT type confusionIncorrect alias information in the IonMonkey JIT compiler when setting array elements can cause a type confusion in Firefox, Firefox ESR and Thunderb…KEVEPSS 46%analysed

Source: NIST National Vulnerability Database (record CVE-2026-5731), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.