webtransport-go: Memory Exhaustion Attack due to Buffering of Unknown Capsules
Exploitation and risk
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cve-program · CVE-2026-57497
Publishedwebtransport-go is an implementation of the WebTransport protocol. Prior to 0.11.1, Session.parseNextCapsule() in session.go skips an unknown WebTransport capsule on the HTTP/3 request stream by calling io.ReadAll on the capsule reader, retaining the complete declared capsule body in memory. A malicious peer can send a large unknown capsule and cause a client or server to allocate memory for the full payload; QUIC flow control does not bound the total retained allocation because reading advances the flow-control window while the received bytes remain in memory. The resulting memory and resource exhaustion can disrupt or crash the affected process. This issue is fixed in version 0.11.1.
- Source published
- 14 Sep 2026 16:05:31 UTC
- Source modified
- 14 Sep 2026 20:06:48 UTC
- Saved here
- 23 Oct 2026 15:48:27 UTC
- Source terms
- CVE Program Terms of Use
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CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
euvd · EUVD-2026-77618
Publishedwebtransport-go is an implementation of the WebTransport protocol. Prior to 0.11.1, Session.parseNextCapsule() in session.go skips an unknown WebTransport capsule on the HTTP/3 request stream by calling io.ReadAll on the capsule reader, retaining the complete declared capsule body in memory. A malicious peer can send a large unknown capsule and cause a client or server to allocate memory for the full payload; QUIC flow control does not bound the total retained allocation because reading advances the flow-control window while the received bytes remain in memory. The resulting memory and resource exhaustion can disrupt or crash the affected process. This issue is fixed in version 0.11.1.
Additional publisher context
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
Original publisher date fields
datePublished: Sep 14, 2026, 4:05:31 PM
dateUpdated: Sep 14, 2026, 8:06:48 PM
- Source published
- Sep 14, 2026, 4:05:31 PM (timezone not stated)
- Source modified
- Sep 14, 2026, 8:06:48 PM (timezone not stated)
- Saved here
- 11 Nov 2026 14:08:37 UTC
- Source terms
- ENISA EUVD · source terms and attribution apply
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EUVD CVSS 3.1 · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
nvd · CVE-2026-57497
Publishedwebtransport-go is an implementation of the WebTransport protocol. Prior to 0.11.1, Session.parseNextCapsule() in session.go skips an unknown WebTransport capsule on the HTTP/3 request stream by calling io.ReadAll on the capsule reader, retaining the complete declared capsule body in memory. A malicious peer can send a large unknown capsule and cause a client or server to allocate memory for the full payload; QUIC flow control does not bound the total retained allocation because reading advances the flow-control window while the received bytes remain in memory. The resulting memory and resource exhaustion can disrupt or crash the affected process. This issue is fixed in version 0.11.1.
Additional publisher context
NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.
Source analysis status: Deferred
Weakness classifications: CWE-770
Original publisher date fields
published: 2026-09-14T17:17:49.097
lastModified: 2026-09-30T17:51:56.193
- Source published
- 14 Sep 2026 17:17:49 UTC
- Source modified
- 30 Sep 2026 17:51:56 UTC
- Saved here
- 25 Oct 2026 14:19:16 UTC
- Source terms
- NIST NVD usage terms; underlying source attribution retained
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CVSS 3.1 · [email protected] · Secondary · 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
osv · GHSA-g35j-m5xg-vh3q
Published## Summary An attacker can cause excessive memory allocation in webtransport-go by sending an unknown WebTransport capsule with a large payload. The implementation skips unknown capsules by reading the entire capsule body into memory, instead of draining it without retaining the data. This can lead to memory exhaustion. ## Impact A misbehaving or malicious peer can cause a denial-of-service (DoS) attack against webtransport-go clients or servers by triggering excessive memory allocation, potentially leading to crashes or resource exhaustion. ## Details WebTransport sessions use capsules on the HTTP/3 request stream. Unknown capsule types are ignored, but the capsule body still needs to be consumed before the next capsule can be parsed. webtransport-go used `io.ReadAll` when skipping unknown capsules. Since the capsule reader is only limited by the capsule's declared length, a peer could send a large unknown capsule and cause the receiver to allocate memory for the full capsule body. QUIC flow control limits buffered data, but it does not bound total allocation here, since reading the stream advances the flow control window while retaining the received bytes in memory. ## The Fix webtransport-go now drains unknown capsules to `io.Discard` instead of buffering them. This consumes the capsule body so parsing can continue, without retaining the payload in memory.
- Source published
- 24 Jul 2026 20:49:28 UTC
- Source modified
- 10 Sep 2026 03:50:51 UTC
- Saved here
- 24 Oct 2026 13:19:41 UTC
- Source terms
- GitHub Advisory Database · CC-BY-4.0
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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Publisher rating · MODERATE
osv · GO-2026-6099
Publishedwebtransport-go: Memory Exhaustion Attack due to Buffering of Unknown Capsules in github.com/quic-go/webtransport-go
- Source published
- 18 Aug 2026 14:32:29 UTC
- Source modified
- 18 Aug 2026 15:00:16 UTC
- Saved here
- 24 Oct 2026 13:19:41 UTC
- Source terms
- OSV · upstream source license applies
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Source: osv · OSV · upstream source license applies. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.