SimpleSAMLphp SP accepts a response from an unexpected IdP when unsigned Response/InResponseTo is combined with a signed assertion lacking SubjectConfirmationData/InResponseTo

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-49284: 0.22% estimated exploitation activity in the next 30 days; percentile 12.89 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary SimpleSAMLphp's SAML SP ACS path does not enforce the IdP selected for an SP-initiated login. If a saved SP state contains ExpectedIssuer = IdP A, but the ACS receives a valid response from IdP B, the code logs a warning and continues processing instead of rejecting the response. That behavior becomes security-relevant when combined with the response-processing rule that accepts an unsigned samlp:Response/@InResponseTo outside the signed assertion whenever the signed assertion's SubjectConfirmationData does not carry its own InResponseTo. A response issued by one trusted IdP can therefore be bound to SP state created for another IdP. Impact In a multi-IdP deployment, a lower-trust IdP can satisfy SP state created for a different expected IdP. This can bypass an SP flow that intentionally routes the user to a specific IdP, including deployments that set enableunsolicited to false to prevent IdP-initiated logins. The impact is highest when the SP trusts multiple IdPs with…

Published by the source

2 Jul 2026, 20:47 UTC

Last modified by the source

2 Jul 2026, 20:47 UTC

Source last checked

26 Oct 2026, 14:49 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-q8r6-xj3f-wrrm

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# Patch Next advisory brief: CVE-2026-49284

Advisory: SimpleSAMLphp SP accepts a response from an unexpected IdP when unsigned `Response/InResponseTo` is combined with a signed assertion lacking `SubjectConfirmationData/InResponseTo`
IDs: CVE-2026-49284, GHSA-q8r6-xj3f-wrrm
Record: https://patchnext.com/advisories/cve-2026-49284 (revision 1, source checked 26 Oct 2026, 14:49 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: simplesamlphp/simplesamlphp 2.5.2, 2.4.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist simplesamlphp/simplesamlphp: affected >= 2.5.0, <= 2.5.1; <= 2.4.6; fixed in 2.5.2, 2.4.7

## Suggested inspection (read-only)
- Packagist simplesamlphp/simplesamlphp: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on simplesamlphp/simplesamlphp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-q8r6-xj3f-wrrm (GitHub-reviewed advisory GHSA-q8r6-xj3f-wrrm lists affected ranges: Packagist simplesamlphp/simplesamlphp >=2.5.0 =0 <=2.4.6)

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