CVE-2026-2781Network attack vector

AES-GCM forgery via overflowed GHASH lengths

Published Feb 24, 2026 · Updated Feb 24, 2026

Integer overflow in NSS in affected Firefox and Thunderbird releases allows attackers to forge large AES-GCM ciphertexts. The gcmHash_Update path multiplies an unsigned 32-bit input length by eight before adding it to 64-bit GHASH counters, truncating bit lengths at 512 MB. Firefox before 148, Firefox ESR before 140.8, Thunderbird before 148, and Thunderbird ESR before 140.8 are affected primarily on ARM64; attackers must observe a ciphertext over 512 MB with aligned associated data.

CVSS severity9.8
Critical
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in NSS in affected Firefox and Thunderbird releases allows attackers to forge large AES-GCM ciphertexts. The gcmHash_Update path multiplies an unsigned 32-bit input length by eight before adding it to 64-bit GHASH counters, truncating bit lengths at 512 MB. Firefox before 148, Firefox ESR before 140.8, Thunderbird before 148, and Thunderbird ESR before 140.8 are affected primarily on ARM64; attackers must observe a ciphertext over 512 MB with aligned associated data.

The record

CVE
CVE-2026-2781
Published
Feb 24, 2026
Updated
Feb 24, 2026
Vendor
Mozilla
Product
Firefox
Classifications
CWE-190, T1565.002
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 <140.8

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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.

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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 exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
T1565.002Transmitted Data Manipulation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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