HOMEVULNERABILITIESCVE-2020-26276
CRITICAL

CVE-2020-26276

CWE-290Published: December 17, 2020· Updated: Jun 17, 2026

9.8
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2020-26276 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Vendors & Products

fleetdm1 product(s)
fleet
Source: NVD CPE · 1 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607
PATCHhttps://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607
ADVISORYhttps://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020
ADVISORYhttps://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcx
ADVISORYhttps://github.com/mattermost/xml-roundtrip-validator
ADVISORYhttps://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities
ADVISORYhttps://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020
ADVISORYhttps://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcx
ADVISORYhttps://github.com/mattermost/xml-roundtrip-validator
ADVISORYhttps://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilities

All References (10)

→
https://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020Release Notes · Third Party Advisory
→
https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607Patch · Third Party Advisory
→
https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcxThird Party Advisory
→
https://github.com/mattermost/xml-roundtrip-validatorThird Party Advisory
→
https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilitiesNot Applicable · Third Party Advisory
→
https://github.com/fleetdm/fleet/blob/master/CHANGELOG.md#fleet-351-dec-14-2020Release Notes · Third Party Advisory
→
https://github.com/fleetdm/fleet/commit/57812a532e5f749c8e18c6f6a652eca65c083607Patch · Third Party Advisory
→
https://github.com/fleetdm/fleet/security/advisories/GHSA-w3wf-cfx3-6gcxThird Party Advisory
→
https://github.com/mattermost/xml-roundtrip-validatorThird Party Advisory
→
https://mattermost.com/blog/coordinated-disclosure-go-xml-vulnerabilitiesNot Applicable · Third Party Advisory

Quick Facts

CVE IDCVE-2020-26276
CVSS Score9.8 / 10
SeverityCRITICAL
WeaknessCWE-290
CISA KEVNo
Affected1 vendor(s)
PublishedDec 17, 2020

Related CVEs (CWE-290)

CVE-2026-6213
10.0
CVE-2026-54782
10.0
CVE-2026-39858
10.0
CVE-2020-5415
10.0
CVE-2025-34063
10.0
CVE-2020-7388
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2020-26276 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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