CVE-2026-21438 Overview
CVE-2026-21438 is a memory leak vulnerability in webtransport-go, an implementation of the WebTransport protocol. Prior to version 0.10.0, an attacker can cause unbounded memory consumption by repeatedly creating and closing many WebTransport streams. Closed streams were not removed from an internal session map, preventing garbage collection of their resources. This vulnerability is classified as CWE-401 (Missing Release of Memory after Effective Lifetime).
Critical Impact
Remote attackers can exhaust server memory resources through repeated WebTransport stream creation and closure, potentially causing denial of service conditions without requiring authentication.
Affected Products
- webtransport-go versions prior to 0.10.0
Discovery Timeline
- 2026-02-12 - CVE-2026-21438 published to NVD
- 2026-02-12 - Last updated in NVD database
Technical Details for CVE-2026-21438
Vulnerability Analysis
This vulnerability stems from improper memory management in the webtransport-go library. When WebTransport streams are created and subsequently closed, the library fails to properly clean up internal data structures. Specifically, closed streams remain in an internal session map indefinitely, which prevents the Go runtime's garbage collector from reclaiming the memory associated with these streams.
The vulnerability requires no authentication and can be exploited remotely over the network. An attacker can continuously open and close WebTransport streams, causing the server's memory footprint to grow unboundedly until system resources are exhausted.
Root Cause
The root cause is CWE-401: Missing Release of Memory after Effective Lifetime. The webtransport-go implementation maintains a session map to track active WebTransport streams. When streams are closed, the corresponding entries in this map are not removed, leading to a memory leak. Without proper cleanup, references to closed stream objects persist, preventing garbage collection and causing memory to accumulate over time.
Attack Vector
The attack can be executed remotely over the network without requiring any privileges or user interaction. An attacker would:
- Establish a connection to a server running the vulnerable webtransport-go library
- Open multiple WebTransport streams in rapid succession
- Close these streams without allowing the server to properly clean up
- Repeat this process to continuously accumulate memory allocations
- Continue until server memory is exhausted, causing denial of service
The vulnerability is particularly concerning for high-traffic services using WebTransport, as legitimate usage patterns could inadvertently trigger the memory leak, while malicious actors could deliberately exploit it for DoS attacks.
Detection Methods for CVE-2026-21438
Indicators of Compromise
- Steadily increasing memory consumption on servers running webtransport-go without corresponding increase in active connections
- Large number of WebTransport stream open/close events from single sources in a short time period
- Server process memory usage growing beyond expected thresholds over time
- Unusual patterns of rapid stream creation and termination in WebTransport logs
Detection Strategies
- Monitor server memory utilization metrics for gradual, unbounded growth patterns
- Implement connection rate limiting and stream creation throttling at the application layer
- Configure alerting on memory consumption thresholds for processes using webtransport-go
- Review application logs for patterns of excessive stream creation and closure from individual clients
Monitoring Recommendations
- Set up continuous memory monitoring for all services using webtransport-go prior to v0.10.0
- Implement logging for WebTransport stream lifecycle events (creation, closure, errors)
- Configure alerts when memory usage exceeds baseline thresholds by a significant margin
- Monitor for denial of service symptoms such as service degradation or out-of-memory errors
How to Mitigate CVE-2026-21438
Immediate Actions Required
- Upgrade webtransport-go to version 0.10.0 or later immediately
- Audit all applications and services to identify those using the vulnerable webtransport-go library
- Implement connection rate limiting to reduce the potential impact of exploitation attempts
- Consider temporarily disabling WebTransport functionality if upgrade is not immediately possible
Patch Information
The vulnerability is fixed in webtransport-go version 0.10.0. The fix ensures that closed streams are properly removed from the internal session map, allowing the garbage collector to reclaim memory resources. Users should upgrade to this version or later to remediate the vulnerability.
For detailed information about the fix, refer to:
Workarounds
- Implement aggressive connection and stream rate limiting at the application or network layer
- Deploy memory usage monitoring with automatic service restarts when thresholds are exceeded
- Consider using a reverse proxy or load balancer to limit the rate of WebTransport connections
- Schedule periodic service restarts during maintenance windows to clear accumulated memory until upgrade is complete
# Example: Update webtransport-go dependency in Go module
go get github.com/quic-go/webtransport-go@v0.10.0
go mod tidy
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
