CVE-2023-6859Public exploitNetwork attack vector

Crash via freed TLS socket layer

Published Dec 19, 2023 · Updated Feb 13, 2025

Use-after-free in Mozilla Firefox before 121, Firefox ESR before 115.6, and Thunderbird before 115.6 allows remote attackers to cause a crash. During TLS socket creation, SSL_SetURL allocation failure destroys plaintextLayer, but error handling later passes that freed layer to PR_GetIdentitiesLayer. Network content must trigger a TLS connection while allocation fails under memory pressure; public testing demonstrated a crash, while code execution was not established.

CVSS severity8.8
High
EPSS probability1.09%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Mozilla Firefox before 121, Firefox ESR before 115.6, and Thunderbird before 115.6 allows remote attackers to cause a crash. During TLS socket creation, SSL_SetURL allocation failure destroys plaintextLayer, but error handling later passes that freed layer to PR_GetIdentitiesLayer. Network content must trigger a TLS connection while allocation fails under memory pressure; public testing demonstrated a crash, while code execution was not established.

The record

CVE
CVE-2023-6859
Published
Dec 19, 2023
Updated
Feb 13, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-416
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 19, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <121

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <121
Mozilla · Thunderbirdversion=unspecified <115.6
Mozilla · Firefox ESRversion=unspecified <115.6

Published CVSS scores

8.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-416Use After Free

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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