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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-65838?
3 open source packages ship an affected version, including github.com/zalando/skipper.
| Package | 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.
Sources
Also known as GHSA-8qqm-fp2q-v734, GO-2026-6019.