# CVE-2026-65838: Skipper: Incomplete fix for CVE-2026-50197: an oversized body can bypass OPA deny-on-presence Rego policies

> Attackers can bypass Open Policy Agent deny rules by sending oversized bodies, allowing forbidden payloads to reach protected services.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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:** 14 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** GHSA-8qqm-fp2q-v734, GO-2026-6019

## What is CVE-2026-65838?

CVE-2026-65838 is a high-severity vulnerability in zalando skipper, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Skipper is an HTTP router and reverse proxy for service composition. Prior to 0.27.35, the opaAuthorizeRequestWithBody filter in filters/openpolicyagent/openpolicyagent.go can allow an oversized declared Content-Length request to bypass a deny-on-presence Rego policy because ExtractHttpBodyOptionally leaves OPA with an empty parsed_body while forwarding the complete request body upstream. This incomplete remediation of CVE-2026-50197 affects deployments that authorize request-body content and exceed -open-policy-agent-max-request-body-size, which defaults to 1 MB. Policy logic that does not reject input.attributes.request.http.truncated_body can therefore fail open and permit a forbidden payload to reach the protected service, while small bodies and the previously fixed chunked-body case are evaluated normally. This issue is fixed in version 0.27.35.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2026-65838?

3 open source packages ship an affected version, including github.com/zalando/skipper.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/zalando/skipper` | Go | All versions | 0.27.26 |
| `github.com/zalando/skipper` | Go | All versions | 0.27.26 |
| `github.com/zalando/skipper` | Go | All versions | 0.27.26 |

## How do I fix CVE-2026-65838?

Upgrade github.com/zalando/skipper to 0.27.26 or later.

## Is CVE-2026-65838 being exploited?

There is no known exploitation of CVE-2026-65838 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-65838 and fix it if it is affected.

What it is: CVE-2026-65838 is a high-severity vulnerability in zalando skipper, published on 14 Sep 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-2026-65838 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/zalando/skipper (Go): affected all versions; fixed in 0.27.26
- github.com/zalando/skipper (Go): affected all versions; fixed in 0.27.26
- github.com/zalando/skipper (Go): affected all versions; fixed in 0.27.26

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-2026-65838/ (Markdown: https://insights.sbomify.com/CVE-2026-65838/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-65838
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-65838
- OSV: https://osv.dev/vulnerability/CVE-2026-65838

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-65838/
Summaries are generated and may contain mistakes; the official description above is the record.