How serious is CVE-2026-21434?

This vulnerability has a CVSS score of 5.3 out of 10, classified as MEDIUM severity. Proof-of-concept exploit code is publicly available, making this an active threat.

Is there exploit code available for CVE-2026-21434?

Yes, proof-of-concept exploit code for CVE-2026-21434 is publicly available on GitHub and security research platforms. This increases the risk of active exploitation.

Which products are affected by CVE-2026-21434?

Check the official CVE details for a complete list of affected products and versions.

How do I fix CVE-2026-21434?

To remediate CVE-2026-21434, check for security patches from the vendor. Apply all available updates and security patches. If no patch is available, implement recommended workarounds or security controls to mitigate the risk.

CVE-2026-21434

Medium

|5.3

Exploit Available

Plain English Summary

AI-powered analysis for quick understanding

An attacker can exploit a flaw in the webtransport-go software to send an excessively large message, causing the system to use up all available memory and potentially crash or slow down. This requires the attacker to send a large payload, but since there’s no limit on the size, they can easily overwhelm the system if they have enough bandwidth.

Technical Description

webtransport-go is an implementation of the WebTransport protocol. From 0.3.0 to 0.9.0, an attacker can cause excessive memory consumption in webtransport-go's session implementation by sending a WT_CLOSE_SESSION capsule containing an excessively large Application Error Message. The implementation does not enforce the draft-mandated limit of 1024 bytes on this field, allowing a peer to send an arbitrarily large message payload that is fully read and stored in memory. This allows an attacker to consume an arbitrary amount of memory. The attacker must transmit the full payload to achieve the memory consumption, but the lack of any upper bound makes large-scale attacks feasible given sufficient bandwidth. This vulnerability is fixed in 0.10.0.

CVSS Vector Analysis

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

Confidentiality ImpactNone

Integrity ImpactNone

Availability ImpactLow

ScopeUnchanged

Vector String

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Exploit Resources

Search for proof-of-concept code and exploit modules

GitHub Search Exploit-DB Nuclei Templates Metasploit Vulners

Official References

NIST NVD

Est. Bounty

$724($500-$1K)

Vendor Response

Grade APatched in 0 days

Quick Information

Published

Feb 12, 2026

8 days ago

Last Modified

Feb 13, 2026

8 days ago