CVE-2026-25156 Vulnerability Analysis & Exploit Details

CVE-2026-25156 Vulnerability Summary

CVE-2026-25156: HotCRP is conference review software. HotCRP versions from October 2025 through January 2026 delivered documents of all types with inline Content-Disposition, causing them to be rendered in the user’s browser rather than downloaded. (The intended behavior was for only `text/plain`, `application/pdf`, `image/gif`, `image/jpeg`, and `image/png` to be delivered inline, though adding `save=0` to the document URL could request inline delivery for any document.) This made users who clicked a document link vulnerable to cross-site scripting attacks. An uploaded HTML or SVG document would run in the viewer’s browser with access to their HotCRP credentials, and Javascript in that document could eventually make arbitrary calls to HotCRP’s API. Malicious documents could be uploaded to submission fields with “file upload” or “attachment” type, or as attachments to comments. PDF upload fields were not vulnerable. A search of documents uploaded to hotcrp.com found no evidence of exploitation. The vulnerability was introduced in commit aa20ef288828b04550950cf67c831af8a525f508 (11 October 2025), present in development versions and v3.2, and fixed in commit 8933e86c9f384b356dc4c6e9e2814dee1074b323 and v3.2.1. Additionally, c3d88a7e18d52119c65df31c2cc994edd2beccc5 and v3.2.1 remove support for `save=0`.

CVE-2026-25156 References

External References

• https://github.com/kohler/hotcrp/commit/8933e86c9f384b356dc4c6e9e2814dee1074b323
• https://github.com/kohler/hotcrp/commit/aa20ef288828b04550950cf67c831af8a525f508
• https://github.com/kohler/hotcrp/commit/c3d88a7e18d52119c65df31c2cc994edd2beccc5
• https://github.com/kohler/hotcrp/security/advisories/GHSA-p88p-2f2p-2476

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• XSS Using MIME Type Mismatch CAPEC-209 An adversary creates a file with scripting content but where the specified MIME type of the file is such that scripting is not expected. The adversary tricks the victim into accessing a URL that responds with the script file. Some browsers will detect that the specified MIME type of the file does not match the actual type of its content and will automatically switch to using an interpreter for the real content type. If the browser does not invoke script filters before doing this, the adversary's script may run on the target unsanitized, possibly revealing the victim's cookies or executing arbitrary script in their browser.
• DOM-Based XSS CAPEC-588 This type of attack is a form of Cross-Site Scripting (XSS) where a malicious script is inserted into the client-side HTML being parsed by a web browser. Content served by a vulnerable web application includes script code used to manipulate the Document Object Model (DOM). This script code either does not properly validate input, or does not perform proper output encoding, thus creating an opportunity for an adversary to inject a malicious script launch a XSS attack. A key distinction between other XSS attacks and DOM-based attacks is that in other XSS attacks, the malicious script runs when the vulnerable web page is initially loaded, while a DOM-based attack executes sometime after the page loads. Another distinction of DOM-based attacks is that in some cases, the malicious script is never sent to the vulnerable web server at all. An attack like this is guaranteed to bypass any server-side filtering attempts to protect users.
• Reflected XSS CAPEC-591 This type of attack is a form of Cross-Site Scripting (XSS) where a malicious script is "reflected" off a vulnerable web application and then executed by a victim's browser. The process starts with an adversary delivering a malicious script to a victim and convincing the victim to send the script to the vulnerable web application.
• Stored XSS CAPEC-592 An adversary utilizes a form of Cross-site Scripting (XSS) where a malicious script is persistently "stored" within the data storage of a vulnerable web application as valid input.
• Cross-Site Scripting (XSS) CAPEC-63 An adversary embeds malicious scripts in content that will be served to web browsers. The goal of the attack is for the target software, the client-side browser, to execute the script with the users' privilege level. An attack of this type exploits a programs' vulnerabilities that are brought on by allowing remote hosts to execute code and scripts. Web browsers, for example, have some simple security controls in place, but if a remote attacker is allowed to execute scripts (through injecting them in to user-generated content like bulletin boards) then these controls may be bypassed. Further, these attacks are very difficult for an end user to detect.
• AJAX Footprinting CAPEC-85 This attack utilizes the frequent client-server roundtrips in Ajax conversation to scan a system. While Ajax does not open up new vulnerabilities per se, it does optimize them from an attacker point of view. A common first step for an attacker is to footprint the target environment to understand what attacks will work. Since footprinting relies on enumeration, the conversational pattern of rapid, multiple requests and responses that are typical in Ajax applications enable an attacker to look for many vulnerabilities, well-known ports, network locations and so on. The knowledge gained through Ajax fingerprinting can be used to support other attacks, such as XSS.

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