# webtransport-go: Memory Exhaustion Attack due to Missing Cleanup of Streams Map

Advisory record · `GHSA-2f2x-8mwp-p2gc`

- **Identifiers:** `GHSA-2f2x-8mwp-p2gc` · `CVE-2026-21438` · `GO-2026-4483`
- **State:** Confirmed
- **Severity:** CVSS 5.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-401](https://cwe.mitre.org/data/definitions/401.html) · [CWE-459](https://cwe.mitre.org/data/definitions/459.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md) · [CWE-459](https://agentprime.io/advisories/tag/cwe-459.md)
- **Published:** 12 Feb 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 12 Feb 2026, 15:29 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `github.com/quic-go/webtransport-go` (Go): affected `<0.10.0`; fixed in `0.10.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> webtransport-go versions before 0.10.0 do not remove closed streams from an internal session map, so memory grows as streams are opened and closed. A remote peer able to open WebTransport streams on a session can exhaust memory this way. Upgrade to version 0.10.0 or later, which removes closed streams from the map. No workaround is listed.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 5.3 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0041, the 35th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:14 UTC: First seen by agentprime
- 31 Oct 2026, 14:14 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-2f2x-8mwp-p2gc)

## Sources

- [GitHub Advisory Database: GHSA-2f2x-8mwp-p2gc](https://github.com/advisories/GHSA-2f2x-8mwp-p2gc)
- [OSV: GHSA-2f2x-8mwp-p2gc](https://osv.dev/vulnerability/GHSA-2f2x-8mwp-p2gc)
- <https://github.com/quic-go/webtransport-go/security/advisories/GHSA-2f2x-8mwp-p2gc>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-21438>
- <https://github.com/quic-go/webtransport-go>
- <https://github.com/quic-go/webtransport-go/releases/tag/v0.10.0>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-2f2x-8mwp-p2gc>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-2f2x-8mwp-p2gc/>. Everything for agents: <https://agentprime.io/llms.txt>.