CVE-2026-57497 in webtransport-go
Summary
by MITRE • 09/14/2026
webtransport-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.
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Analysis
by VulDB Data Team • 09/14/2026
The webtransport-go library serves as a Go implementation of the WebTransport protocol, which facilitates low-latency, bidirectional communication over HTTP/3 and QUIC connections. In versions prior to 0.11.1, a critical resource management flaw exists within the Session.parseNextCapsule function located in session.go. This vulnerability arises from how the library handles unknown or unrecognized capsule types received during an active WebTransport session. When the parser encounters a capsule type it does not recognize, rather than discarding the data immediately to conserve resources, it proceeds to read the entire declared body of that capsule into memory using io.ReadAll.
This design choice creates a significant security risk because it allows for unbounded memory allocation based on external input. A malicious peer can exploit this behavior by sending a WebTransport capsule with an unknown type and declaring an extremely large payload size in the header. Upon receiving such a request, the affected client or server will allocate heap memory sufficient to hold the entire declared payload, regardless of whether that data is actually needed for processing. This allocation occurs even though the application logic has no intention of utilizing this specific capsule, making it a pure resource consumption attack vector rather than one leading directly to code execution.
The severity of this vulnerability is compounded by the interaction between Go's memory management and QUIC flow control mechanisms. In standard HTTP/3 or QUIC implementations, flow control windows are designed to limit the amount of data that can be sent without acknowledgment, thereby preventing a sender from overwhelming a receiver with too much data at once. However, in this specific implementation flaw, reading the capsule advances the QUIC receive window as bytes are consumed by io.ReadAll. This means the connection appears healthy and flow control is satisfied, allowing the attacker to continue sending large amounts of data without triggering standard congestion controls or backpressure mechanisms that might otherwise limit the stream size.
Consequently, the received bytes remain resident in memory while the application continues to process subsequent packets. If an attacker sends multiple such malformed capsules with large declared sizes, the target system will rapidly exhaust its available RAM. This leads to a denial of service condition where the affected Go process may become unresponsive due to garbage collection pressure or crash entirely when it fails to allocate further required memory structures. The impact is particularly severe for long-lived WebTransport connections that are expected to handle high volumes of traffic, as even small numbers of malicious capsules can destabilize the host environment over time.
This vulnerability aligns with CWE-400, which describes uncontrolled resource consumption, specifically focusing on excessive allocation or retention of resources leading to denial of service. From a tactical perspective, this attack vector corresponds to ATT&CK technique T1498.002, Network Denial of Service via Resource Exhaustion by Application Layer Protocol Abuse. The attacker leverages the legitimate protocol features for capsule parsing and flow control advancement to bypass standard network-level defenses that monitor bandwidth or packet rates but do not inspect application-layer memory allocation patterns.
To mitigate this risk, organizations using webtransport-go must upgrade immediately to version 0.11.1 or later, where the logic has been corrected to prevent retaining large unknown payloads in memory. For environments unable to patch immediately, defensive measures should include implementing strict limits on capsule sizes at a proxy or gateway layer before traffic reaches the vulnerable application server. Additionally, monitoring for unusually high memory consumption patterns associated with WebTransport sessions can help detect active exploitation attempts. It is also advisable to review QUIC flow control configurations and ensure that applications do not rely solely on network-level controls for resource management when dealing with untrusted peer inputs in protocol implementations.