CVE-2023-6857Network attack vector

Incorrect file access via truncated symlink target

Published Dec 19, 2023 · Updated Feb 13, 2025

A symlink race in Mozilla Firefox before 121, Firefox ESR before 115.6, and Thunderbird before 115.6 allows remote attackers to misdirect file access. The XPCOM nsLocalFileUnix::GetNativeTarget method sizes a buffer from lstat, then fails to detect when readlink fills it after a link grows, silently accepting a truncated target. Exploitation requires user interaction and winning the timing race on Android, Linux, or macOS; Windows is unaffected, and the resulting operation uses the wrong filesystem path.

CVSS severity5.3
Medium
EPSS probability0.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A symlink race in Mozilla Firefox before 121, Firefox ESR before 115.6, and Thunderbird before 115.6 allows remote attackers to misdirect file access. The XPCOM nsLocalFileUnix::GetNativeTarget method sizes a buffer from lstat, then fails to detect when readlink fills it after a link grows, silently accepting a truncated target. Exploitation requires user interaction and winning the timing race on Android, Linux, or macOS; Windows is unaffected, and the resulting operation uses the wrong filesystem path.

The record

CVE
CVE-2023-6857
Published
Dec 19, 2023
Updated
Feb 13, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-362
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

6.1Amazon LinuxCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
5.3NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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