CVE-2026-108546 in Spotweb
Summary
by MITRE • 10/10/2026
Spotweb through 1.5.8 contains an OS command injection vulnerability in the runcommand NZB handler that allows remote attackers to execute commands by publishing spots with malicious titles. Attackers can post self-signed spots over Usenet with shell metacharacters in the title, which are substituted unescaped for $SPOTTITLE and passed to exec() when a user downloads the spot, running commands as the Spotweb PHP process.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 10/10/2026
The vulnerability identified in Spotweb versions through 1.5.8 represents a critical server-side security flaw classified under CWE-78, which denotes Improper Neutralization of Special Elements used in an OS Command. This specific weakness manifests within the runcommand NZB handler, a component responsible for processing Newzbin-style binary files downloaded from Usenet servers. The core technical failure lies in the application's handling of user-supplied input derived directly from published spot titles. When a remote attacker publishes a maliciously crafted spot over the Usenet network, they can embed shell metacharacters within the title field. These characters are not properly sanitized or escaped before being processed by the backend PHP logic.
During the operational workflow, when an authenticated user initiates a download of this compromised spot, the application retrieves the untrusted title data and substitutes it into a variable designated as $SPOTTITLE. This variable is subsequently passed directly to the exec() function without any validation or filtering mechanisms in place. Because the input contains executable shell commands rather than benign text, the operating system interprets these sequences as valid instructions. Consequently, this allows for arbitrary command execution on the host server running the Spotweb instance. The severity of this issue is compounded by the fact that the executed commands run with the same privileges as the PHP process itself, which often possesses significant access rights to the file system and network resources depending on how the web server or application container is configured.
From an offensive security perspective, this vulnerability aligns closely with MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter sub-techniques such as sh (T1059.004) or bash (T1059.004). An attacker can leverage the injected commands to perform reconnaissance, escalate privileges by exploiting local vulnerabilities, pivot into internal networks if the server has broader connectivity, or exfiltrate sensitive data stored on the machine. The attack vector is particularly insidious because it relies on social engineering elements inherent in Usenet culture, where users are encouraged to share and download content based on titles, making them likely candidates for triggering the vulnerability unknowingly.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most effective solution is to upgrade Spotweb to a version later than 1.5.8, where this input validation flaw has been patched by properly escaping or rejecting special characters in user-supplied fields before they reach system-level functions. In environments where upgrading is not immediately feasible, administrators should implement strict input validation at the application layer using allowlists for expected character sets in spot titles. Additionally, deploying a Web Application Firewall with rules capable of detecting and blocking shell metacharacters in HTTP parameters or data streams can provide an additional layer of defense. It is also critical to ensure that the PHP process runs under a restricted user account with minimal permissions, thereby limiting the potential impact if command injection occurs. Regular security audits focusing on all instances where external input interacts with OS commands are essential to prevent similar CWE-78 vulnerabilities in other parts of the application.