How severe is CVE-2020-26276?

CVE-2020-26276 has a CVSS 3.x base score of 10.0, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2020-26276 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-26276?

CVE-2020-26276 affects Fleetdm Fleet. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2020-26276?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2020-26276 published?

CVE-2020-26276 was published on 2020-12-17 and last updated on 2026-06-17.

CVE-2020-26276

CVE-2020-26276 is a critical-severity vulnerability in Fleetdm Fleet with a CVSS 3.x base score of 10.0. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-290.

Key facts

Severity: Critical (CVSS 3.x base score 10.0)
CVSS v2: 6.8
EPSS exploit prediction: 2% (80th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-290
Affected product: Fleetdm Fleet
Published: 2020-12-17
Last modified: 2026-06-17

Description

Fleet is an open source osquery manager. In Fleet before version 3.5.1, due to issues in Go's standard library XML parsing, a valid SAML response may be mutated by an attacker to modify the trusted document. This can result in allowing unverified logins from a SAML IdP. Users that configure Fleet with SSO login may be vulnerable to this issue. This issue is patched in 3.5.1. The fix was made using https://github.com/mattermost/xml-roundtrip-validator If upgrade to 3.5.1 is not possible, users should disable SSO authentication in Fleet.

Frequently asked questions

What is CVE-2020-26276?: Fleet is an open source osquery manager. In Fleet before version 3.5.1, due to issues in Go's standard library XML parsing, a valid SAML response may be mutated by an attacker to modify the trusted document. This can result in allowing unverified logins from a SAML IdP. Users that configure Fleet with SSO login may be vulnerable to this issue. This issue is patched in 3.5.1. The fix was made using https://github.com/mattermost/xml-roundtrip-validator If upgrade to 3.5.1 is not possible, users should disable SSO authentication in Fleet.
How severe is CVE-2020-26276?: CVE-2020-26276 has a CVSS 3.x base score of 10.0, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2020-26276 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-26276?: CVE-2020-26276 affects Fleetdm Fleet. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2020-26276?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2020-26276 published?: CVE-2020-26276 was published on 2020-12-17 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:fleetdm:fleet:*:*:*:*:*:*:*:*

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