CVE-2026-2790Public exploitNetwork attack vector

Script execution via double-decoded JAR filenames

Published Feb 24, 2026 · Updated Feb 24, 2026

Same-origin policy bypass in Mozilla Firefox and Thunderbird before 148 and ESR before 140.8 allows attackers to execute script from crafted JAR files. The Networking: JAR channel inconsistently decodes and normalizes archive-entry names, then content-sniffs an unknown type instead of requiring its extension. Execution requires a crafted ZIP or JAR and user navigation to a double-encoded jar: URL; attacker-controlled HTML or JavaScript then runs under the misidentified resource.

CVSS severity8.8
High
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Same-origin policy bypass in Mozilla Firefox and Thunderbird before 148 and ESR before 140.8 allows attackers to execute script from crafted JAR files. The Networking: JAR channel inconsistently decodes and normalizes archive-entry names, then content-sniffs an unknown type instead of requiring its extension. Execution requires a crafted ZIP or JAR and user navigation to a double-encoded jar: URL; attacker-controlled HTML or JavaScript then runs under the misidentified resource.

The record

CVE
CVE-2026-2790
Published
Feb 24, 2026
Updated
Feb 24, 2026
Vendor
Mozilla
Product
Firefox
Classifications
CWE-346, T1204.002
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

8.8CISA-ADPCVSS:3.1/AV:N/AC:L/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 exploitPublished

Weakness, pattern, technique

CWE-346Origin Validation Error
T1204.002Malicious File

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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