CVE-2026-2775Network attack vector

Unspecified impact via HTML parser mitigation bypass

Published Feb 24, 2026 · Updated Feb 24, 2026

Mitigation bypass in Mozilla Firefox and Thunderbird allows remote attackers to cause unspecified impact through browser-like content. The affected releases are Firefox before 148, Firefox ESR before 115.33 and before 140.8, and Thunderbird before 148 and before 140.8; Mozilla has not disclosed which DOM HTML Parser mitigation is bypassed or which parser operation mishandles input. Thunderbird normally blocks this path through email because scripting is disabled while messages are read, although browser and browser-like contexts remain exposed.

CVSS severity9.8
Critical
EPSS probability0.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Mitigation bypass in Mozilla Firefox and Thunderbird allows remote attackers to cause unspecified impact through browser-like content. The affected releases are Firefox before 148, Firefox ESR before 115.33 and before 140.8, and Thunderbird before 148 and before 140.8; Mozilla has not disclosed which DOM HTML Parser mitigation is bypassed or which parser operation mishandles input. Thunderbird normally blocks this path through email because scripting is disabled while messages are read, although browser and browser-like contexts remain exposed.

The record

CVE
CVE-2026-2775
Published
Feb 24, 2026
Updated
Feb 24, 2026
Vendor
Mozilla
Product
Firefox
Classifications
CWE-288
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 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 <148

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <148
Mozilla · Thunderbirdversion=unspecified <140.8; version=unspecified <148
Mozilla · Firefox ESRversion=unspecified <115.33; version=unspecified <140.8

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/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
9.8NIST NVDCVSS: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-288Authentication Bypass Using an Alternate Path or Channel

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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