CVE-2026-65838

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.

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.

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:

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:

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).

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.

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.

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:

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:

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).

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