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Vulnerabilities

Vulnerability · CVE-2023-6858

Firefox was susceptible to a heap buffer overflow in due to insufficient OOM handling.

Published Dec 19, 2023 · catalog updated Oct 26, 2026 · Firefox was susceptible to

Last checked Nov 4, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2023-6858. EPSS is 1.54%. Act only if a listed version of Firefox was susceptible to is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Firefox was susceptible to).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Unknown—
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
1.54%
Remediation
Advisory link
Affected products
Debian:12 firefox-esr · Debian:12 thunderbird · Debian:13 firefox-esr · Debian:13 thunderbird · Debian:14 firefox-esr · Debian:14 thunderbird

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

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • Debian:12 firefox-esr0 → 115.6.0esr-1~deb12u1
  • Debian:12 thunderbird0 → 1:115.6.0-1~deb12u1
  • Debian:13 firefox-esr0 → 115.6.0esr-1
  • Debian:13 thunderbird0 → 1:115.6.0-1
  • Debian:14 firefox-esr0 → 115.6.0esr-1
  • Debian:14 thunderbird0 → 1:115.6.0-1

How to fix CVE-2023-6858

  • Upgrade

    CVE-2023-6858 lists a fix boundary at 115.6.0esr-1~deb12u1. Compare the installed build with that boundary before you change production.

  • Version check

    Fixed in 115.6.0esr-1~deb12u1 · 5 other ranges on the advisory

  • Advisory

    Open the cve_org record and follow its fix.

  • Official advisories

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2023-6858. EPSS is 1.54%. Act only if a listed version of Firefox was susceptible to is installed.

Which versions are affected?

Compare what you have installed with 0 → 115.6.0esr-1~deb12u1, 0 → 1:115.6.0-1~deb12u1, 0 → 115.6.0esr-1, 0 → 1:115.6.0-1. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 1.54%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Debian security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Dec 19, 2023 · OpenSSF OSV / OSV Scanner

    Detected

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

  2. Oct 26, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    firefox-esr fixed in 115.6.0esr-1~deb12u1; firefox-esr fixed in 115.6.0esr-1; firefox-esr fixed in 115.6.0esr-1; thunderbird fixed in 1:115.6.0-1~deb12u1

  3. Oct 26, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    firefox-esr fixed in 115.6.0esr-1~deb12u1

  4. Oct 26, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    firefox-esr fixed in 115.6.0esr-1

  5. Oct 26, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    thunderbird fixed in 1:115.6.0-1~deb12u1

  6. Oct 26, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    thunderbird fixed in 1:115.6.0-1

  7. Oct 26, 2026 · OpenSSF OSV / OSV Scanner

    Updated

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

Sources

References

Freshness

Last verified in this catalog Nov 4, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • CVE.orgOct 27, 2026
  • OpenSSF OSV / OSV ScannerOct 26, 2026