Is CVE-2026-21435 actively exploited?

No active exploitation of CVE-2026-21435 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2026-21435 be exploited remotely?

Yes. CVE-2026-21435 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2026-21435?

CVE-2026-21435 has a CVSS score of 5.3 (MEDIUM) and an EPSS exploitation probability of 0.02%.

HOME VULNERABILITIESCVE-2026-21435

MEDIUM

CVE-2026-21435

CWE-400Published: February 12, 2026· Updated: Feb 13, 2026

5.3

CVSS v3.1

EPSS:0.02%probability of exploitation in 30 daysPercentile:4.2th

Official Description

webtransport-go is an implementation of the WebTransport protocol. Prior to v0.10.0, an attacker can cause a denial of service in webtransport-go by preventing or indefinitely delaying WebTransport session closure. A malicious peer can withhold QUIC flow control credit on the CONNECT stream, blocking transmission of the WT_CLOSE_SESSION capsule and causing the close operation to hang. This vulnerability is fixed in v0.10.0.

NVD Source

Technical Analysis

CVE-2026-21435 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.