# CVE-2026-15981: SAML Single Sign On <= 5.4.4 - Unauthenticated Authentication Bypass via SAMLResponse Parameter

> Unauthenticated attackers can bypass SAML signature verification to log in as any user, including administrators, due to a flawed boolean check.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 23 Jul 2026
- **Updated:** 24 Jul 2026
- **Also known as:** GHSA-wgjx-q85h-87v2

## What is CVE-2026-15981?

CVE-2026-15981 is a critical authentication bypass vulnerability in cyberlord92 SAML Single Sign On – SSO Login, published on 23 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The SAML Single Sign On – SSO Login plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 5.4.4. This is due to the mo_saml_validate_signature() function performing a loose boolean check on the raw tri-state integer returned by PHP's openssl_verify(), causing an error return value of -1 to be evaluated as truthy and therefore treated as a successful signature verification. This makes it possible for unauthenticated attackers to log in as any existing WordPress user, including administrators, by submitting a crafted SAMLResponse containing an attacker-controlled NameID and a deliberately malformed signature value that triggers an OpenSSL processing error — bypassing verification entirely and resulting in wp_set_auth_cookie() being called for the targeted account.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2026-15981?


## How do I fix CVE-2026-15981?

No fix has been published for CVE-2026-15981 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-15981 being exploited?

There is no known exploitation of CVE-2026-15981 in the wild and no public exploit code.

Public exploit code:

- SAML Single Sign On <= 5.4.4 - Unauthenticated Authentication Bypass via SAMLResponse Parameter (github_poc): https://github.com/Nxploited/CVE-2026-15981
- https://github.com/katranSefa/CVE-2026-15981 (github_poc): https://github.com/katranSefa/CVE-2026-15981

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-15981 and fix it if it is affected.

What it is: CVE-2026-15981 is a critical authentication bypass vulnerability in cyberlord92 SAML Single Sign On – SSO Login, published on 23 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-15981 in the wild and no public exploit code.

Affected product: cyberlord92 SAML Single Sign On – SSO Login. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-15981/ (Markdown: https://insights.sbomify.com/CVE-2026-15981/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-15981
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-15981
- OSV: https://osv.dev/vulnerability/CVE-2026-15981

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-15981/
Summaries are generated and may contain mistakes; the official description above is the record.