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Horde IMP through 6.2.27, when used with Horde Application Framework through 5.2.23, is vulnerable to cross-site scripting via crafted text/html e-mail content. According to the provided content, an attacker can send an HTML e-mail message containing an onerror attribute, including variants that use base64-encoded JavaScript, which is then executed when the message is rendered in the webmail interface. The issue affects HTML e-mail handling/rendering and results in script execution in the context of the victim's authenticated Horde session. The vulnerability was reportedly exploited in the wild in March 2025.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository demonstrates a proof-of-concept exploit for a stored XSS vulnerability in the Horde Web Client (Horde 5.2.23 with IMP 6.2.27). The exploit leverages the ability to inject a specially crafted HTML payload into an email, which, when viewed in the Horde webmail interface, triggers JavaScript execution via the onerror event of an <img> tag. The payload is obfuscated using Unicode and hexadecimal encoding to evade detection. The repository contains three files: Details.md (explains the vulnerability and payload construction), PoC.py (Python script to send a malicious email with the XSS payload), and README.md (overview and usage notes). The main attack vector is a zero-click email-based XSS, requiring only that the victim views the email in the vulnerable web client. The exploit does not target desktop email clients. The PoC payload is benign (logs to console), but the technique allows for arbitrary JavaScript execution, which could be weaponized for credential theft or mailbox compromise.
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