# CVE-2026-16728: undici vulnerable to downstream response desynchronization via retry interceptor

> A malicious upstream can cause response desynchronization in undici's retry interceptor, leading to connection hangs or corrupted data in proxy applications.

- **Severity:** Medium 4.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Jul 2026
- **Updated:** 30 Jul 2026
- **Also known as:** CLEANSTART-2026-CJ83222, CLEANSTART-2026-HI60053, CLEANSTART-2026-VN19790, DEBIAN-CVE-2026-16728, ECHO-cad4-7176-7840, GHSA-8xcm-r25x-g524, MINI-25hw-vw66-gx3x, MINI-2mgg-7vmp-g69r, MINI-36m7-j7p5-jjqq, MINI-3xw3-f74g-hjf4, MINI-4h4c-xq2f-rhmf, MINI-4mg5-ff75-mcm5, MINI-6cjc-jcj6-gqf5, MINI-72qj-gw53-x7qf, MINI-748f-2hpg-2768, MINI-777w-x28q-rcc7, MINI-8v2c-6jw3-353p, MINI-f92f-f9cc-6hpp, MINI-fwx3-r996-532g, MINI-g4cq-cm2f-rrmh, MINI-h4rh-9xwj-2r7r, MINI-hgw6-g3hp-gx5v, MINI-hmr9-qcqr-3qgm, MINI-mw8h-q93j-f532, MINI-pghc-h39j-xvp6, MINI-ph8r-f3w2-m8qq, MINI-qhgh-vrff-gj9m, MINI-rch9-6vvg-25x5, MINI-rwm6-qp87-85rg, MINI-wwhq-hq7c-f9m8, ROOT-APP-NPM-CVE-2026-16728, UBUNTU-CVE-2026-16728

## What is CVE-2026-16728?

CVE-2026-16728 is a medium-severity vulnerability in Nodejs Undici, published on 29 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

undici's retry interceptor can deliver a response whose body length does not match the Content-Length header exposed to the application after a retry or resume of a partial response. In undici before 6.28.0, from 7.0.0 up to before 7.29.0, and from 8.0.0 up to before 8.9.0, a malicious or faulty upstream can return a partial response with a mismatched framing header, close the socket early, and have the retry interceptor assemble a body of a different length while the original Content-Length stays attached. Applications that use the retry interceptor and forward upstream headers and bodies downstream, such as proxies or gateways, may then emit an invalid HTTP response with a stale Content-Length, leading to downstream response desynchronization, connection hangs, or response corruption. Exploitation requires the retry interceptor enabled, an upstream returning a mismatched partial response, and a downstream forwarder that does not remove or recalculate Content-Length. The issue is fixed in undici 6.28.0, 7.29.0, and 8.9.0.

Weakness: CWE-444 (Inconsistent Interpretation of HTTP Requests)

## Which versions are affected by CVE-2026-16728?

6 open source packages ship an affected version, including undici. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `undici` | npm | All versions | 6.28.0 |
| `undici` | npm | All versions | 6.28.0 |
| `undici` | npm | From 7.0.0 | 7.29.0 |
| `undici` | npm | From 7.0.0 | 7.29.0 |
| `undici` | npm | From 8.0.0 | 8.9.0 |
| `undici` | npm | From 8.0.0 | 8.9.0 |

Products: Nodejs Undici.

## How do I fix CVE-2026-16728?

Upgrade undici to a fixed version for your release line: 6.28.0, 7.29.0 or 8.9.0.

## Is CVE-2026-16728 being exploited?

There is no known exploitation of CVE-2026-16728 in the wild and no public exploit code.

## Other vulnerabilities in Nodejs Undici

- [CVE-2026-109855](https://insights.sbomify.com/CVE-2026-109855/): undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake (high 7.5)
- [CVE-2026-109869](https://insights.sbomify.com/CVE-2026-109869/): undici vulnerable to Denial of Service via unhandled error on excessive content-encodings (high 7.5)
- [CVE-2026-87018](https://insights.sbomify.com/CVE-2026-87018/): undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation (high 7.5)
- [CVE-2026-19534](https://insights.sbomify.com/CVE-2026-19534/): undici vulnerable to Denial of Service via unrequested WebSocket subprotocol (high 7.5)
- [CVE-2026-12151](https://insights.sbomify.com/CVE-2026-12151/): undici WebSocket client vulnerable to denial of service via fragment count bypass (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-16728 and fix it if it is affected.

What it is: CVE-2026-16728 is a medium-severity vulnerability in Nodejs Undici, published on 29 Jul 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-2026-16728 in the wild and no public exploit code.

Affected packages and fixed versions:
- undici (npm): affected all versions; fixed in 6.28.0
- undici (npm): affected all versions; fixed in 6.28.0
- undici (npm): affected from 7.0.0; fixed in 7.29.0
- undici (npm): affected from 7.0.0; fixed in 7.29.0
- undici (npm): affected from 8.0.0; fixed in 8.9.0
- undici (npm): affected from 8.0.0; fixed in 8.9.0

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-2026-16728/ (Markdown: https://insights.sbomify.com/CVE-2026-16728/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-16728
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-16728
- OSV: https://osv.dev/vulnerability/CVE-2026-16728

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-16728/
Summaries are generated and may contain mistakes; the official description above is the record.