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

Quick assessment

Affected
quic-go webtransport-go
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

webtransport-go是quic-go开源的一个Go语言库。 webtransport-go 0.10.0之前版本存在安全漏洞，该漏洞源于未强制执行应用错误消息字段的大小限制，可能导致内存消耗过大。

CVSS 5.3 · Medium EPSS 0.46% · P39

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking
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I. Basic Information for CVE-2026-21434

Vulnerability Information
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Vulnerability Title
webtransport-go affected by Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
不加限制或调节的资源分配
Source: CVE Program / CVE List V5
Vulnerability Title
webtransport-go 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
webtransport-go是quic-go开源的一个Go语言库。 webtransport-go 0.10.0之前版本存在安全漏洞，该漏洞源于未强制执行应用错误消息字段的大小限制，可能导致内存消耗过大。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
quic-go webtransport-go < 0.10.0 -

II. Public POCs for CVE-2026-21434

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III. Intelligence Information for CVE-2026-21434

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Vendor Advisories for CVE-2026-21434 (1)

Same Patch Batch · quic-go · 2026-02-12 · 3 CVEs total

CVE-2026-21435 5.3 MEDIUM webtransport-go CloseWithError can block indefinitely
CVE-2026-21438 5.3 MEDIUM webtransport-go affected by a Memory Exhaustion Attack due to Missing Cleanup of Streams M

IV. Related Vulnerabilities

Same product: webtransport-go
Same vendor: quic-go
Same weakness: CWE-770

V. Comments for CVE-2026-21434

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