Answer in brief
CVE-2026-117553 records a High severity (CVSS 7.7) vulnerability in Umbraco CMS before 17.7.2 and 18.2.2 Account Takeover via Host Header Poisoning. The current sources do not mark it as known exploited. The current feed maps umbraco/Umbraco-CMS (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.7. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps umbraco/Umbraco-CMS (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| umbraco/Umbraco-CMSgeneric | >=0 <17.7.2 || >=18.0.0 <18.2.2 | 17.7.2, 18.2.2 |
Published upstream
Oct 27, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Oct 27, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Oct 27, 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.
Quoted source text, attributed separately from HOL analysis.