Skipper: an oversized declared-`Content-Length` body still hands OPA an empty `parsed_body`, so deny-on-presence Rego policies fail OPEN while the full payload reaches upstream

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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.

Source published

14 Sep 2026 20:01:27 UTC

Source modified

15 Sep 2026 13:55:41 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

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.

Source published

Sep 14, 2026, 8:01:27 PM (timezone not stated)

Source modified

Sep 15, 2026, 1:55:41 PM (timezone not stated)

Observed here

11 Nov 2026 15:08:22 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

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.

Source published

14 Sep 2026 20:16:49 UTC

Source modified

16 Sep 2026 13:42:48 UTC

Observed here

25 Oct 2026 15:18:45 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

### Summary A wrong policy can be an open door. You have to check `input.attributes.request.http.truncated_body` in your policy. ### Description Incomplete fix for CVE-2026-50197: an oversized declared-`Content-Length` body still hands OPA an empty `parsed_body`, so deny-on-presence Rego policies fail OPEN while the full payload reaches upstream. The CVE-2026-50197 fix (commit `3152f3b0`, PR #4041, v0.26.10) substituted `expectedSize = maxBodyBytes` only when `req.ContentLength < 0` (chunked / HTTP/2 without content-length). But when a request declares a `Content-Length` larger than `maxBodyBytes`, `expectedSize > maxBodyBytes`, the body-extraction `if` is skipped entirely, and `ExtractHttpBodyOptionally` returns `rawBodyBytes = nil` — so OPA evaluates an empty `parsed_body`, while the full forbidden payload still flows to the upstream. A deny-on-presence policy (`default allow = true; allow = false if input.parsed_body.<forbidden>`) — the exact Rego shape the advisory describes — fails OPEN. The fix's own comment reasons only about `ContentLength == -1`; the oversized branch was never considered, and the added PoC test only covers small bodies. ### Affected code - `filters/openpolicyagent/openpolicyagent.go` `ExtractHttpBodyOptionally`: the `expectedSize <= maxBodyBytes` gate lets an oversized declared body fall through to `return req.Body, nil, func() {}, nil` (OPA sees an empty document). - Corroborated by Skipper's own unit test "Read body exhausting max bytes" (`{ "welcome": "world" }`, `maxBodySize: 5` → `bodyInPolicy: ""`). ### Steps to reproduce See attached `docker-compose.yml` (official `golang` image) + `setup.sh` + `exploit.sh`, which run a real Skipper proxy (`proxytest`) with a real OPA control plane (`opasdktest`), `WithMaxRequestBodyBytes(32)`, policy `allow = false if input.parsed_body.action == "delete"`, route `* -> opaAuthorizeRequestWithBody("test") -> upstream`: - `{"action":"delete"}` (19B ≤ 32) → **403** (denied). - `{"action":"delete","pad":"X..64"}` (> 32) → **200**, upstream received the full body (BYPASS). - small chunked `{"action":"delete"}` → **403** (positive control: the original CVE is fixed). (Library-tier: validated via Skipper's real proxy test harness, not a deploy of the official image; benign oracle = status diff + upstream-received body; no RCE.) ### Impact Deployments authorizing on request-body content via `opaAuthorizeRequestWithBody` + deny-on-presence Rego can be bypassed by inflating the request body past `-open-policy-agent-max-request-body-size` (default 1 MB); the full payload still reaches the upstream. ### Mitigation Document how policy owners should block requests with oversized body. Example deny by default and use "allow if" no oversized body: ```rego default allow := false allow if { input.attributes.request.http.truncated_body == false # ... body-based conditions } ``` Example allow by default and use "deny if" an oversized body: ```rego default deny := false deny if { input.attributes.request.http.truncated_body == true # ... body-based conditions } ``` Documentation is published by https://github.com/zalando/skipper/releases/tag/v0.27.26 ### Credit Reported as part of an incomplete-patch measurement study (responsible disclosure).

Source published

17 Jul 2026 21:49:48 UTC

Source modified

25 Sep 2026 17:15:05 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

Publisher rating · HIGH

Skipper: Incomplete fix for CVE-2026-50197: an oversized body can bypass OPA deny-on-presence Rego policies in github.com/zalando/skipper

Source published

22 Jul 2026 20:36:35 UTC

Source modified

15 Sep 2026 11:55:56 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.