Horizon Alert
Summary of the vulnerability and why it matters
A vulnerability exists in the http4k toolkit for Kotlin applications that affects how certain XML data is processed. While previous fixes addressed some risks, a residual gap allowed for denial-of-service attacks through a specific type of XML manipulation, even if other malicious external entities were blocked. The latest update rejects any XML documents containing doctype declarations, mitigating this remaining risk. The main concern is confirming relevance and exposure.
- Malicious XML can crash services.
- Prevents complex internal XML attacks.
- Confirm if your Kotlin HTTP apps use http4k.
Attack Path
How an attacker could exploit the issue
An attacker could target applications built with http4k by sending specially crafted XML data within an HTTP request. If the application uses http4k's XML parsing functions, the attacker could leverage this to cause a denial-of-service condition by overwhelming the server with complex entity expansions.
- Requires network access to the application.
- Triggered by sending malicious XML in HTTP requests.
- Risk of denial-of-service attacks.
Live Threat
Current exploitation, exposure, and threat context
When http4k applications process untrusted XML content in requests, they could be vulnerable to denial-of-service attacks that exhaust server resources. This could occur when an application uses `Body.xml()` or `Document.asXmlDocument()` to parse specially crafted XML documents containing `<!DOCTYPE>` declarations.
- Denial-of-service attacks.
- Malicious XML documents.
- Service disruption or unavailability.
Priority actions
Operational Fix
Recommended remediation, mitigation, and detection steps
In a real-world scenario, application owners and platform teams are likely responsible for addressing this vulnerability within their Kotlin HTTP applications that use the http4k library. The first practical step involves identifying all instances of the affected http4k XML parsing functionality, confirming their accessibility and criticality, and then coordinating remediation efforts.
- Application owners should own the issue.
- Verify XML parsing usage and reachability.
- Plan remediation or vendor coordination.
