CVE-2023-6858

Name: CVE-2023-6858
Creator: NVD / NIST
Published: 2023-12-19T14:15:07.42+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.8/10EPSS 1.53%

Last modified Jun 17, 2026

CVE-2023-6858 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. Firefox was susceptible to a heap buffer overflow in `nsTextFragment` due to insufficient OOM handling. This vulnerability affects Firefox ESR < 115.6, Thunderbird < 115.6, and Firefox < 121.. EPSS estimates a 1.53% chance of exploitation in the next 30 days.

Description

Firefox was susceptible to a heap buffer overflow in `nsTextFragment` due to insufficient OOM handling. This vulnerability affects Firefox ESR < 115.6, Thunderbird < 115.6, and Firefox < 121.

Metrics

CVSS 3.1

8.8/10

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

EPSS Probability

1.53%

71.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 121.0
Mozilla	Firefox Esr	< 115.6
Mozilla	Thunderbird	< 115.6
Debian	Debian Linux	10.0
Debian	Debian Linux	11.0
Debian	Debian Linux	12.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1826791Issue Tracking, Permissions Required
https://lists.debian.org/debian-lts-announce/2023/12/msg00020.htmlMailing List, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/12/msg00021.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202401-10Third Party Advisory
https://www.debian.org/security/2023/dsa-5581Third Party Advisory
https://www.debian.org/security/2023/dsa-5582Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2023-54/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2023-55/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2023-56/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1826791Issue Tracking, Permissions Required
https://lists.debian.org/debian-lts-announce/2023/12/msg00020.htmlMailing List, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/12/msg00021.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202401-10Third Party Advisory
https://www.debian.org/security/2023/dsa-5581Third Party Advisory
https://www.debian.org/security/2023/dsa-5582Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2023-54/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2023-55/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2023-56/Vendor Advisory

Timeline

Published: Dec 19, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-6858?

Firefox was susceptible to a heap buffer overflow in `nsTextFragment` due to insufficient OOM handling. This vulnerability affects Firefox ESR < 115.6, Thunderbird < 115.6, and Firefox < 121.

How severe is CVE-2023-6858?

CVE-2023-6858 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 1.53% probability of exploitation in the next 30 days.

How do I fix CVE-2023-6858?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2023-6858?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST