Stirling-PDF CVE-2026-33437

Exploitation requires three specific conditions to align: the Stirling-PDF instance must be running a version prior to 2.0.0; the attacker must be able to introduce a crafted PDF (with a malicious payload in the Title or Author metadata) into the system, either by uploading it directly or by inducing a victim to upload it; and the victim must actively click 'Get Info' on that specific PDF file within the Stirling-PDF UI. The CVSS vector (PR:N) reflects that the attacker requires no credentials on the Stirling-PDF instance itself - payload delivery is out-of-band via the PDF file. However, the victim must be an authenticated session holder on the instance for session-theft impact to materialize, since there is no pre-authentication exposure surface. User interaction (UI:R) is non-waivable: the XSS does not trigger on upload or passive file listing, only on the explicit 'Get Info' action. Single-user self-hosted deployments face negligible real-world risk because an attacker would need to target the same person who operates the instance.

The CVSS 8.1 score is consistent with the mechanics: network delivery (AV:N), low complexity (AC:L), no attacker-side privileges required (PR:N), required victim interaction (UI:R), unchanged scope (S:U), and high confidentiality and integrity impact reflecting session compromise and DOM manipulation. The two-step delivery chain - attacker provides crafted PDF, victim must click 'Get Info' - meaningfully reduces opportunistic exploitation risk compared to a zero-click path. No EPSS score was provided in the source data, so exploitation probability cannot be quantified. The absence of a KEV listing and any POC reference suggests no confirmed widespread or automated exploitation at time of analysis. Risk is highest for multi-user or team-shared Stirling-PDF deployments where untrusted PDFs regularly flow through the system; single-user self-hosted deployments face materially lower practical risk since the attacker and victim would need to be different people. The v2.0.0 major release also introduces significant licensing changes, which may complicate upgrade timelines for some organizations.

An attacker crafts a PDF file using a scripting library (e.g., PyPDF2 or pikepdf) that embeds a JavaScript payload such as a cookie-stealing script inside the document's Title or Author metadata field. The attacker delivers this PDF to a target who operates a shared Stirling-PDF instance - for example, via email, a shared drive, or a phishing lure framed as a legitimate document - and the victim uploads it and clicks 'Get Info' to inspect the file's properties. The payload executes in the victim's authenticated browser session, potentially exfiltrating session tokens to an attacker-controlled server or performing actions within the Stirling-PDF interface on the victim's behalf.