CVE-2026-8956
Published: May 19, 2026· Updated: May 20, 2026
Official Description
Integer overflow in the Networking: JAR component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.
Risk Analysis
This critical vulnerability in Mozilla Firefox and Thunderbird stems from an integer overflow in the Networking: JAR component, allowing for potential remote code execution. With a CVSS score of 9.8, this flaw is extremely severe, indicating a high impact on confidentiality, integrity, and availability. The absence of an EPSS score means the exploitation likelihood is currently undetermined.
No public exploit is currently known for this vulnerability. Its network attack vector and low attack complexity indicate it is remotely exploitable without user interaction.
To address this vulnerability, users must upgrade to Firefox 151, Firefox ESR 140.11, Thunderbird 151, or Thunderbird 140.11. Promptly applying these updates is essential to protect against potential exploitation.
Technical Analysis
CVE-2026-8956 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.
The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.
A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.
CVSS v3.1 Vector Breakdown
Affected Vendors & Products
Exploit & PoC Resources
Official Patches & Advisories
All References (5)
Quick Facts
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2026-8956 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts