We're two months into 2026 and a webmail vulnerability that should've stayed dead is back in the wild. According to SecurityWeek, a flaw in RoundCube Webmail that received a patch last December is being actively exploited in real attacks right now. This isn't theoretical. It's happening.
The vulnerability is an XSS attack vector hiding in SVG documents—specifically through animate tags. For anyone running RoundCube instances without that December patch, this is a problem that needs immediate attention.
What We Know
The timeline here matters. RoundCube patched this vulnerability in December 2025. Two months later, we're seeing active exploitation in the wild. That's not a long window for attackers to weaponize something, which suggests either the patch details leaked early or threat actors were already probing.
It's an XSS vulnerability.
That means attackers can inject malicious scripts into webmail sessions without direct server compromise. The attack vector is particularly nasty because it s SVG animate tags—something that doesn't immediately scream "security risk" to administrators doing quick security reviews. Most organizations are looking for obvious stuff. They're not always thinking about how SVG animations could become a cyber attack vector.
SecurityWeek has documented active exploitation. This isn't speculation or proof-of-concept code floating around—actual attacks are happening against actual systems.
How It Works
Here's the technical breakdown. An attacker crafts an SVG document containing an animate tag with malicious JavaScript embedded in it. When a RoundCube user views that SVG document through their webmail interface, the animate tag executes in the context of their webmail session. That's your XSS attack cyber security problem right there.
Why animate tags specifically? Because they're often overlooked in input validation and content filtering. Security teams focus on script tags, iframe injections, event handlers like onclick. An animate tag doesn't look like a typical XSS attack vector. It looks like legitimate SVG markup.
Once the JavaScript executes, attackers have access to whatever that user can access in their webmail—session cookies, email content, contact information, forwarding rules. They could establish persistence, extract credentials, or pivot into backend systems.
Why It Matters
So why does this matter beyond the obvious? Because RoundCube is widely deployed. It's open-source, it's trusted, and it's running in enterprise environments across the world. This isn't some fringe webmail client.
The real question is why we're seeing active exploitation two months post-patch. That suggests a significant portion of RoundCube installations are still vulnerable. Whether that's due to patching delays, missed updates, or administrators who don't realize they're running outdated versions—doesn't matter. The result is the same: exposed systems.
This is particularly nasty because it's a xss cyber attack that bypasses traditional security awareness training. You can't tell your users to "just be careful what you click" because the malicious content is embedded in the webmail interface itself. The attack happens server-side when the vulnerable system processes the SVG file.
And it's worth comparing this to similar cyber attack company examples we've seen before. Organizations that suffered webmail compromise through XSS vulnerabilities didn't just lose email access—they lost credential harvesting capabilities, business intelligence, and sometimes their entire email infrastructure became a pivot point for lateral movement.
Next Steps
First: check your RoundCube version immediately. If you're running anything older than the December 2025 patch, you're at risk. This isn't optional.
Second: look for signs of cyber attack in your webmail logs. Unusual SVG uploads, XML submissions, or POST requests containing animate tags should trigger incident response. Check for suspicious forwarding rules created without authorization.
Third: if you can't patch immediately, disable SVG rendering in RoundCube until you can apply updates. Most users don't need to view SVG documents in their webmail anyway.
Finally, use this as a case study in your vulnerability management program. A patch that's two months old and still seeing active exploitation means your patch deployment windows are too long. Adjust accordingly.