VulnerabilityAnalyzed

CVE-2026-59898

Prior to versions 4.1.136.Final and 4.2.16.Final, ab attacker can force WebSocket upgrade via the lax V07 (or V08) handshaker by sending `Sec-WebSocket-Version: 7` and omitting `Connection: Upgrade` / `Upgrade: websocket` headers, completing a protocol…

MEDIUM 6.3EPSS 0.25%

Does this matter?

Lower severity and a low EPSS score (0.25%). Track it; it rarely justifies an emergency change on its own.

Description

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, ab attacker can force WebSocket upgrade via the lax V07 (or V08) handshaker by sending `Sec-WebSocket-Version: 7` and omitting `Connection: Upgrade` / `Upgrade: websocket` headers, completing a protocol switch that a proxy would not recognize as an Upgrade request and enabling HTTP request smuggling / protocol-confusion attacks. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

CVSS 4.0: 6.3 MEDIUMCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
EPSS: 0.25% probability · 16th percentile
CISA KEV: Not listed
Weakness: CWE-444
Affected: netty/netty
Source: security-advisories@github.com

References

https://github.com/netty/netty/releases/tag/netty-4.1.136.FinalRelease Notes
https://github.com/netty/netty/releases/tag/netty-4.2.16.FinalRelease Notes
https://github.com/netty/netty/security/advisories/GHSA-4mp9-239f-g9hgVendor Advisory

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.