CVE-2026-49284 — simplesamlphp
HIGHCVE-2026-49284 is a high-severity (CVSS 7.1) CWE-345 vulnerability in simplesamlphp/simplesamlphp. A fix is available for simplesamlphp/simplesamlphp — see the affected versions and patch details below.
SimpleSAMLphp SP accepts a response from an unexpected IdP when unsigned `Response/InResponseTo` is combined with a signed assertion lacking `SubjectConfirmationData/InResponseTo`
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-49284.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-49284 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 390,400 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
simplesamlphp/simplesamlphp🐘simplesamlphp/simplesamlphpReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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 enable_unsolicited to false to prevent IdP-initiated logins.
The impact is highest when the SP trusts multiple IdPs with different assurance levels, tenant boundaries, or attribute namespaces, and application authorization depends on the selected/expected IdP. In those deployments this is an authentication/authorization bypass candidate. Impact strongly depends on whether an attacker can obtain a signed IdP-initiated assertion from a lower-trust trusted IdP and whether the downstream application maps identifiers globally.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | simplesamlphp/simplesamlphp | ≥ 2.5.0&&< 2.5.2 | 2.5.2composer require simplesamlphp/simplesamlphp:^2.5.2 |
| 🐘Packagist | simplesamlphp/simplesamlphp | all versions | 2.4.7composer require simplesamlphp/simplesamlphp:^2.4.7 |
Affected Products
simplesamlphpsimplesamlphpDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for simplesamlphp/simplesamlphp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update simplesamlphp/simplesamlphp to 2.5.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-49284 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-49284 in your dependencies?
Find it across Packagist, including transitive dependencies.