7.5

CVE-2026-21434: webtransport-go affected by Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule

Analyzed
AliasesCGA-29f4-868r-7m7jCGA-2p83-jr3v-2596CGA-2q66-pp6j-gc2m
Published 12-02-2026Last modified 12-02-2026

Vulnerability summary

CVE-2026-21434 is a high (CVSS 7.5) vulnerability in quic-go webtransport-go. EPSS estimates a 0.46% chance of exploitation in the next 30 days, higher than 40.3% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 5.3, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
7.5/10
010
High · v3.1 (NVD)
EPSS score
0.46%
0%100%
Low · +0.03 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 2 · Related 3
OPENSUSE-SU-2026:21483-1SUSE-SU-2026:0757-1CGA-76HJ-3QW4-9H2V

Timeline

  1. 12-02-2026
    PublishedVulnerability first disclosed.
  2. 12-02-2026
    Last modifiedVulnerability information updated.

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 metrics

5 scores · 5 sources · 1 version

EPSS trend

Probability

0.46%

Chance of exploitation in the next 30 days

Percentile

40%

Versus all other CVEs

30-day change

Increase +0.03 pp

From 0.44% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Chainguard18 products
  • ipfs-cluster< 1.1.5-r5
  • ipfs-cluster-fips< 1.1.5-r4
  • k3s< 1.35.1.1-r1
  • k3s-1.31< 1.31.6.1-r13
  • k3s-1.32< 1.32.13.1-r2
Wolfi9 products
  • ipfs-cluster< 1.1.5-r5
  • k3s< 1.35.1.1-r1
  • k3s-1.32< 1.32.13.1-r2
  • k3s-1.33< 1.33.9.1-r3
  • k3s-static< 1.35.1.1-r1
Github.com/marten-seemann1 product
  • webtransport-go≥ 0.3.0 (No fix recorded)
Github.com/quic-go1 product
  • webtransport-go≥ 0.3.0, < 0.10.0 | < 0.10.0
Quic-go1 product

5 vendors · 30 products

References

5 links