CVE-2026-2806Public exploitNetwork attack vector

Heap-data exposure via unchecked gzip length

Published Feb 24, 2026 · Updated Feb 24, 2026

Uninitialized-memory use in Mozilla Firefox and Thunderbird before 148 allows remote attackers to access heap data via a malicious font. The gfxSVGGlyphsDocument constructor trusts the gzip trailer length, allocates that size, then passes bytes beyond inflate output to ParseDocument. Attacker-controlled web content must load the font; ordinary Thunderbird email reading disables scripting, and no recovery of heap contents is demonstrated.

CVSS severity9.1
Critical
EPSS probability0.39%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uninitialized-memory use in Mozilla Firefox and Thunderbird before 148 allows remote attackers to access heap data via a malicious font. The gfxSVGGlyphsDocument constructor trusts the gzip trailer length, allocates that size, then passes bytes beyond inflate output to ParseDocument. Attacker-controlled web content must load the font; ordinary Thunderbird email reading disables scripting, and no recovery of heap contents is demonstrated.

The record

CVE
CVE-2026-2806
Published
Feb 24, 2026
Updated
Feb 24, 2026
Vendor
Mozilla
Product
Firefox
Classifications
CWE-908, CWE-457, T1203
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 <148

Published CVSS scores

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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-908Use of Uninitialized Resource
CWE-457Use of Uninitialized Variable
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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