Summary
YOURLS: Unauthenticated File Inclusion
YOURLS versions ≤1.10.4 contain an unauthenticated path traversal vulnerability that allows attackers to include and execute arbitrary PHP files on the server without any credentials.
Details
The vulnerability exists because YOURLS uses URL sanitization functions (yourls_sanitize_url(), yourls_esc_url()) to filter request paths, but these functions are designed to clean URLs, not filesystem paths. They preserve / and . characters, allowing ../ sequences to pass through unfiltered.
The unsanitized keyword is then directly concatenated into a filesystem path and passed to file_exists() and later include() operations, enabling path traversal attacks.
Data Flow:
HTTP Request URI (with ../)
↓
yourls_get_request() (no sanitization)
↓
yourls_sanitize_url() (preserves / and .)
↓
yourls_esc_url() (permits / and . via regex)
↓
Keyword extraction (preserves ../)
↓
file_exists(YOURLS_PAGEDIR . "/$keyword.php") ← Sink
↓
include(YOURLS_PAGEDIR . "/$keyword.php") ← Code Execution
Proof of Concept (POC)
In the concept validation, we assume that the attacker has uploaded a test.php file to the web root directory, but it cannot be accessed directly. (Of course, it could also be any path, such as /tmp/test.php)
Setup
Place a test file in web root:
./test.php:
<?php
phpinfo();
?>
Attack Request
GET /../../test HTTP/1.1
Host: target.com
Connection: close
Response (Apache Environment)
Impact
Remote execution of uploaded PHP files, An attacker uploads a malicious PHP file to an arbitrary location on the server (e.g., via another vulnerability or file upload feature), obtains its absolute path but cannot access it directly. The attacker then leverages this vulnerability to include and execute the PHP file, gaining code execution privileges.
Indirect triggering of PHP code injection, If a PHP code injection point exists on the system (e.g., log injection, session injection) but the injected file cannot be accessed directly due to configuration restrictions, the attacker can use this vulnerability to include and execute the injected code, achieving remote command execution or further compromise.
CVE-2026-62858 has a CVSS score of 5.3 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.10.5); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-62858? CVE-2026-62858 is a medium-severity security vulnerability in yourls/yourls (composer), affecting versions <= 1.10.4. It is fixed in 1.10.5.
- How severe is CVE-2026-62858? CVE-2026-62858 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of yourls/yourls are affected by CVE-2026-62858? yourls/yourls (composer) versions <= 1.10.4 is affected.
- Is there a fix for CVE-2026-62858? Yes. CVE-2026-62858 is fixed in 1.10.5. Upgrade to this version or later.
- Is CVE-2026-62858 exploitable, and should I be worried? Whether CVE-2026-62858 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-62858 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-62858? Upgrade
yourls/yourlsto 1.10.5 or later.