CVE-2026-8389Public exploitNetwork attack vector

Code execution via truncated JIT bytecode offset

Published May 12, 2026 · Updated May 12, 2026

Type confusion in Firefox before 150.0.3 allows remote attackers to execute code after a user opens a page containing crafted JavaScript. On the eager off-thread BaselineJIT path, RetAddrEntry stores an oversized bytecode offset in a 28-bit pcOffset field without a release-build length check, silently truncating it. Exception unwinding then uses the wrong in-bounds bytecode position, reads an incorrect stack slot as an object, and enables code execution within the browser sandbox.

CVSS severity8.8
High
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Type confusion in Firefox before 150.0.3 allows remote attackers to execute code after a user opens a page containing crafted JavaScript. On the eager off-thread BaselineJIT path, RetAddrEntry stores an oversized bytecode offset in a 28-bit pcOffset field without a release-build length check, silently truncating it. Exception unwinding then uses the wrong in-bounds bytecode position, reads an incorrect stack slot as an object, and enables code execution within the browser sandbox.

The record

CVE
CVE-2026-8389
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-733, CWE-119, CWE-686, CWE-843, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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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
7.5redhat-SADPCVSS:3.1/AV:N/AC:H/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 exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-733Compiler Optimization Removal or Modification of Security-critical Code
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-686Function Call With Incorrect Argument Type
CWE-843Access of Resource Using Incompatible Type ('Type Confusion')
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

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Your stack

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