CVE-2026-7840
In your normal cycle
Critical by CVSS (9.8), but no sign of active exploitation.
Description
UltraVNC repeater through 1.8.2.2 contains a global buffer overflow in its embedded HTTP administration server. The functions wi_senderr() and wi_replyhdr() in repeater/webgui/webutils.c write the caller-supplied HTTP request URI into a fixed 1000-byte global buffer (hdrbuf) via unchecked sprintf calls. The HTTP receive buffer accepts URIs up to approximately 150 KB (WI_RXBUFSIZE = 153600), so an unauthenticated attacker who can reach the repeater HTTP port (default TCP 80) can overflow hdrbuf by at least 500 bytes with a single HTTP request containing a URI of 1500 bytes or longer, corrupting adjacent .bss-segment globals. The overflow occurs before any authentication check, making it reachable without credentials. A remote, unauthenticated attacker can achieve arbitrary code execution on the host running the repeater.
Scoring
| CVSS | 9.8 (CRITICAL, v3.1) |
|---|---|
| Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| EPSS | 2.63% — more likely to be exploited than 85% of all CVEs |
| Weakness | CWE-787 |
| On CISA KEV | no |
| Public exploit | none known |
| Published | 2026-07-01 |
| Last modified | 2026-07-09 |
Affected (1)
| Vendor | Product |
|---|---|
| uvnc | ultravnc |
References
→ the Explorer · watch your stack · NVD