CVE-2026-49283
HIGHDescription
The SimpleSAMLphp SAML2 library is a PHP library for SAML2 related functionality. Prior to versions 4.19.3, 4.20.2, 5.0.6, and 6.2.1, the HTTPArtifact::receive() flow can treat an unsigned embedded SAML Response as cryptographically valid for the wrong identity provider. SOAPClient::addSSLValidator() attaches a TLS-based validator to the outer SOAP ArtifactResponse, while the embedded Response receives a validator that delegates to the outer message and is later checked against metadata selected from the embedded response issuer rather than necessarily the artifact issuer. SOAPClient::validateSSL() returns normally when the TLS public key does not match the key being validated, and SAML2\Message::validate() treats a validator call that does not throw as successful. In a multi-IdP federation, a malicious or lower-trust IdP can therefore provide an ArtifactResponse containing an unsigned Response that claims a higher-trust victim IdP as issuer and authenticate as arbitrary users with attacker-chosen assertion attributes, NameID, and session data. This issue is fixed in versions 4.19.3, 4.20.2, 5.0.6, and 6.2.1.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:N
Exploit Intelligence
Low risk: more likely to be exploited than 27% of all known CVEs.
References
Related Vulnerabilities
Other CWE-295 (Improper Certificate Validation) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2015-4000 | Low | 3.7 | 100% | - | Fix |
| CVE-2020-0601 | High | 8.1 | 89% | KEV | Fix |
| CVE-2009-3555 | Critical | 9.8 | 87% | - | Fix |
| CVE-2022-26923 | High | 8.8 | 84% | KEV | Fix |
| CVE-2023-27823 | Critical | 9.8 | 53% | - | - |
| CVE-2022-42979 | High | 8.8 | 24% | - | - |
Common questions
How do I fix CVE-2026-49283?
No published fix for CVE-2026-49283 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-49283 being actively exploited?
Not that we know of. CVE-2026-49283 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.34% is the estimated probability that it will be exploited in the next 30 days. That is higher than 27% of all scored CVEs.
How severe is CVE-2026-49283?
CVE-2026-49283 has a CVSS v3 base score of 8.7, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-19.