PatchTheCVECVE-2021-27736: FusionAuth fusionauth-samlv2 before 0.5.4 allows XXE attacks via a forged AuthnRequest or LogoutRequest becaus
CVE-2021-27736 is a medium-severity flaw (CVSS 6.5) affecting saml v2. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
FusionAuth fusionauth-samlv2 before 0.5.4 allows XXE attacks via a forged AuthnRequest or LogoutRequest because parseFromBytes uses javax.xml.parsers.DocumentBuilderFactory unsafely.
Why this priority
- Public exploit reference
A fixed release or distro patch exists.
Risk facts
| CVSS score | 6.5 (Medium) |
| Attack vector | Network (remote) |
| Attack complexity | Low |
| Privileges needed | Low |
| User interaction | None |
| EPSS exploit chance | 1.3% (top 29%) |
| CISA exploited list | No |
| Weakness | CWE-611 |
| Published | 2021-04-22 |
| Last modified | 2026-06-17 |
Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Published CVE record published
- Updated Record last modified
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2021-27736?
saml v2: upgrade to 0.5.4. Exact commands for each OS are on this page.
Is CVE-2021-27736 being exploited?
CVE-2021-27736 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2021-27736 affect?
CVE-2021-27736 affects saml v2. Severity is medium (CVSS 6.5). FusionAuth fusionauth-samlv2 before 0.5.4 allows XXE attacks via a forged AuthnRequest or LogoutRequest because parseFromBytes uses javax.xml.parsers.DocumentBuilderFactory unsafely.
How urgent is CVE-2021-27736?
Priority 45/100. Public exploit reference