CVE-2025-4919Known exploitationPublic exploitNetwork attack vector

Arbitrary code execution via flawed bounds-check elimination

Published May 17, 2025 · Updated Apr 13, 2026

Out-of-bounds access in Mozilla Firefox before 138.0.4 allows remote attackers to execute code via crafted JavaScript. IonMonkey's TryEliminateBoundsCheck merges bounds checks after ExtractLinearSum applies wrapping 32-bit arithmetic, permitting a crafted huge typed array to access memory before its buffer. Thunderbird before 128.10.2 and 138.0 through 138.0.1 is also affected, but ordinary email reading disables scripting; exploitation requires a browser-like context and remains inside the renderer sandbox.

CVSS severity8.8
High
EPSS probability8.63%
Next 30 days · Sep 16, 2026
Known exploitationReported
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

Out-of-bounds access in Mozilla Firefox before 138.0.4 allows remote attackers to execute code via crafted JavaScript. IonMonkey's TryEliminateBoundsCheck merges bounds checks after ExtractLinearSum applies wrapping 32-bit arithmetic, permitting a crafted huge typed array to access memory before its buffer. Thunderbird before 128.10.2 and 138.0 through 138.0.1 is also affected, but ordinary email reading disables scripting; exploitation requires a browser-like context and remains inside the renderer sandbox.

The record

CVE
CVE-2025-4919
Published
May 17, 2025
Updated
Apr 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, CWE-125, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 17, 2025CVE publishedPublication date reported by the CVE source.
  2. Apr 13, 2026Record 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.8CISA-ADPCVSS: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.

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 exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
CWE-125Out-of-bounds Read
T1203Exploitation for Client Execution

Public exploit references

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

Reported exploitation

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