Quick answers
- Is CVE-2026-7840 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-7840 being exploited in the wild.
- How severe is CVE-2026-7840?
- Critical severity, with a CVSS score of 9.8, published 1 July 2026.
- Which products and versions are affected?
- UltraVNC Repeater through 1.8.2.2.
- Is there a fix for CVE-2026-7840?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-7840 attacked?
- It is attacked over the network, in a network appliance.
- Am I affected by CVE-2026-7840?
- Check whether you run UltraVNC Repeater at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
A global buffer overflow exists in the embedded HTTP administration server of UltraVNC Repeater through version 1.8.2.2. The vulnerability is located in the wi_senderr() and wi_replyhdr() functions within repeater/webgui/webutils.c, which use unchecked sprintf calls to write the HTTP request URI into a fixed 1000-byte global buffer (hdrbuf). While the buffer is small, the HTTP receive buffer accepts URIs up to 150 KB, allowing an unauthenticated remote attacker to overflow the buffer by sending a URI longer than 1500 bytes. This results in the corruption of adjacent .bss-segment globals and can be leveraged to achieve arbitrary code execution. The flaw is reachable on the default TCP port 80 before any authentication checks occur.
Affected products
- UltraVNC UltraVNC Repeater through 1.8.2.2
Timeline
- 2026-07-01: advisory: NVD publication date