CVE-2026-117553
Published:October 27, 2026
Updated:October 29, 2026
Umbraco CMS before 17.7.2 and 18.2.2 contains an authentication bypass vulnerability that allows unauthenticated attackers to register attacker-controlled OAuth redirect URIs by poisoning the Host header. Attackers send signed-in users authorization links using response_mode=form_post to capture codes, then redeem them via HTTP Basic client credentials to hijack back-office sessions and execute code through Razor templates.
Affected Packages
Umbraco.Cms.Api.Management (DOT_NET):
Affected version(s) >=17.0.0.123 <17.7.2Fix Suggestion:
Update to version 17.7.2Umbraco.Cms.Api.Management (DOT_NET):
Affected version(s) >=18.0.0.263 <18.2.2Fix Suggestion:
Update to version 18.2.2https://github.com/umbraco/Umbraco-CMS.git (GITHUB):
Affected version(s) >=release-17.0.0 <release-17.7.2Fix Suggestion:
Update to version release-17.7.2https://github.com/umbraco/Umbraco-CMS.git (GITHUB):
Affected version(s) >=release-18.0.0 <release-18.2.2Fix Suggestion:
Update to version release-18.2.2umbraco.cms (NUGET):
Affected version(s) >=17.0.0 <17.7.2Fix Suggestion:
Update to version 17.7.2umbraco.cms.api.management (NUGET):
Affected version(s) >=17.0.0 <17.7.2Fix Suggestion:
Update to version 17.7.2umbraco.cms (NUGET):
Affected version(s) >=18.0.0 <18.2.2Fix Suggestion:
Update to version 18.2.2umbraco.cms.api.management (NUGET):
Affected version(s) >=18.0.0 <18.2.2Fix Suggestion:
Update to version 18.2.2Related Resources (6)
Do you need more information?
Contact UsCVSS v4
Base Score:
7.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
PASSIVE
Vulnerable System Confidentiality
HIGH
Vulnerable System Integrity
HIGH
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Weakness Type (CWE)
URL Redirection to Untrusted Site
EPSS
Base Score:
0.50