# CVE-2026-21438: webtransport-go affected by a Memory Exhaustion Attack due to Missing Cleanup of Streams Map

> An attacker can cause unbounded memory consumption and denial of service by repeatedly creating and closing WebTransport streams in webtransport-go.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Feb 2026
- **Updated:** 17 Feb 2026
- **Also known as:** GHSA-2f2x-8mwp-p2gc, GO-2026-4483, MINI-5cj6-55r7-xgw5, MINI-p475-v953-fhcq

## What is CVE-2026-21438?

CVE-2026-21438 is a medium-severity denial of service vulnerability in quic-go webtransport-go, published on 12 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

webtransport-go is an implementation of the WebTransport protocol. Prior to 0.10.0, an attacker can cause unbounded memory consumption 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 fixed in v0.10.0.

Weakness: CWE-459 (Incomplete Cleanup), CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2026-21438?

3 open source packages ship an affected version, including github.com/quic-go/webtransport-go. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/quic-go/webtransport-go` | Go | All versions | 0.10.0 |
| `github.com/quic-go/webtransport-go` | Go | All versions | 0.10.0 |
| `github.com/quic-go/webtransport-go` | Go | All versions | 0.10.0 |

Products: Quic-Go Webtransport-Go.

## How do I fix CVE-2026-21438?

Upgrade github.com/quic-go/webtransport-go to 0.10.0 or later.

## Is CVE-2026-21438 being exploited?

There is no known exploitation of CVE-2026-21438 in the wild and no public exploit code.

## Other vulnerabilities in quic-go webtransport-go

- [CVE-2026-21434](https://insights.sbomify.com/CVE-2026-21434/): webtransport-go affected by Memory Exhaustion Attack due to Missing Length Check in WT_CLOSE_SESSION Capsule (medium 5.3)
- [CVE-2026-21435](https://insights.sbomify.com/CVE-2026-21435/): webtransport-go CloseWithError can block indefinitely (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21438 and fix it if it is affected.

What it is: CVE-2026-21438 is a medium-severity denial of service vulnerability in quic-go webtransport-go, published on 12 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-21438 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/quic-go/webtransport-go (Go): affected all versions; fixed in 0.10.0
- github.com/quic-go/webtransport-go (Go): affected all versions; fixed in 0.10.0
- github.com/quic-go/webtransport-go (Go): affected all versions; fixed in 0.10.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-21438/ (Markdown: https://insights.sbomify.com/CVE-2026-21438/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21438
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21438
- OSV: https://osv.dev/vulnerability/CVE-2026-21438

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21438/
Summaries are generated and may contain mistakes; the official description above is the record.