CVE-2026-4721Network attack vector

Code execution via undisclosed memory corruption

Published Mar 24, 2026 · Updated Mar 24, 2026

Memory corruption in Firefox before 149, Firefox ESR before 115.34 or 140.9, and Thunderbird before 149 or 140.9 allows remote attackers to execute code. Mozilla identifies multiple memory-safety defects with observed corruption, but the public bug list does not disclose each faulty operation or input path. Normal browsing can reach the browser flaws; Thunderbird disables scripting while reading mail, limiting exposure there to browser or browser-like contexts.

CVSS severity9.8
Critical
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in Firefox before 149, Firefox ESR before 115.34 or 140.9, and Thunderbird before 149 or 140.9 allows remote attackers to execute code. Mozilla identifies multiple memory-safety defects with observed corruption, but the public bug list does not disclose each faulty operation or input path. Normal browsing can reach the browser flaws; Thunderbird disables scripting while reading mail, limiting exposure there to browser or browser-like contexts.

The record

CVE
CVE-2026-4721
Published
Mar 24, 2026
Updated
Mar 24, 2026
Vendor
Mozilla
Product
Firefox
Classifications
CWE-825, CWE-120, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 24, 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?

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

  1. Affected versionversion=unspecified <149

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <149
Mozilla · Thunderbirdversion=unspecified <140.9; version=unspecified <149
Mozilla · Firefox ESRversion=unspecified <115.34; version=unspecified <140.9

Published CVSS scores

7.5redhat-SADPCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-825Expired Pointer Dereference
CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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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