Horizon Alert
Summary of the vulnerability and why it matters
This critical vulnerability in the Algernon web server could allow unauthenticated attackers to execute arbitrary code remotely by tricking the server into running a malicious script. The issue arises when Algernon searches for a specific configuration file in parent directories, potentially accessing sensitive system functions. This could have significant implications for any deployed instances of the web server.
- Unauthenticated code execution via web requests.
- Matters if you use Algernon web server technology.
- Confirm if Algernon is deployed and exposed.
Attack Path
How an attacker could exploit the issue
An attacker can achieve remote code execution by placing a malicious `handler.lua` file in a directory that Algernon's web server can access. When a user requests a URL that maps to a directory lacking an index file, Algernon searches upwards for this `handler.lua` file. If found, it executes the file with full privileges, granting the attacker control over the server.
- Entry: Attacker places `handler.lua` in accessible directory.
- Trigger: Requesting a directory without an index file.
- Risk: Full remote code execution and server control.
Live Threat
Current exploitation, exposure, and threat context
When Algernon is asked for a directory path without an index file, it may search upwards through parent directories, potentially past the server root, to find a `handler.lua` file to execute. If found, this file is executed with the full Algernon API exposed, allowing for remote code execution. This vulnerability is reachable without authentication, as the handler resolution occurs before permission checks, and any URL pointing to a directory without an index can trigger the search.
- Sensitive system commands and data could be exposed.
- Remote code execution via crafted HTTP requests.
- Compromise of the underlying server and its services.
Operational Fix
Recommended remediation, mitigation, and detection steps
This vulnerability in Algernon's directory traversal allows for unauthenticated remote code execution. Identifying all instances of Algernon, assessing their exposure and criticality, and confirming ownership are the crucial first steps for remediation.
- Application owners should manage remediation.
- Verify Algernon's network exposure.
- Plan remediation during maintenance windows.
