High 7.5Published Oct 27, 2026

CVE-2026-117553Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning

Updated under an hour ago (Oct 28, 2026, 10:30 PM ET)

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It affects Umbraco-CMS. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-601
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: VulnCheck
NVD analysis: Awaiting Analysis
Record last updated: Oct 27, 2026
First seen by InfoSec Signals: Oct 27, 2026

Affected products

Affected products

umbraco Umbraco-CMS umbraco:cms (from the name)	before 17.7.2; from 18.0.0 before 18.2.2	CNA record

References

References

https://github.com/umbraco/Umbraco-CMS/commit/490b9b27dcbb8fb3fe868a36203590968b0569d6	patch
https://github.com/umbraco/Umbraco-CMS	product
https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-rpv9-qp4c-g469	vendor-advisory
https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.1/src/Umbraco.Cms.Api.Management/Middleware/BackOfficeAuthorizationInitializationMiddleware.cs#L74-L112	technical-description
https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.2-and-18.2.2-account-takeover-via-host-header-poisoning	third-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.