CVE-2023-5171Public exploitNetwork attack vector

Application crash via Ion compiler use-after-free

Published Sep 27, 2023 · Updated Feb 13, 2025

Use-after-free in Mozilla Firefox before 118, Firefox ESR before 115.3, and Thunderbird before 115.3 allows remote attackers to crash the application. Ion bailout bookkeeping keeps an untraced parent-child script pointer; garbage collection can finalize the script before a folded-stub update dereferences it and writes two NUL bytes. Reaching the flaw requires attacker-controlled JavaScript to undergo Ion compilation; Thunderbird disables scripting in email, limiting exposure to browser-like contexts.

CVSS severity6.5
Medium
EPSS probability1.03%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Use-after-free in Mozilla Firefox before 118, Firefox ESR before 115.3, and Thunderbird before 115.3 allows remote attackers to crash the application. Ion bailout bookkeeping keeps an untraced parent-child script pointer; garbage collection can finalize the script before a folded-stub update dereferences it and writes two NUL bytes. Reaching the flaw requires attacker-controlled JavaScript to undergo Ion compilation; Thunderbird disables scripting in email, limiting exposure to browser-like contexts.

The record

CVE
CVE-2023-5171
Published
Sep 27, 2023
Updated
Feb 13, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-416, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 27, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=unspecified <118

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <118
Mozilla · Thunderbirdversion=unspecified <115.3
Mozilla · Firefox ESRversion=unspecified <115.3

Published CVSS scores

6.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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.

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

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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
T1203Exploitation for Client Execution

Public exploit references

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo