CVEvulnerability
CVE-2026-7840
9.3 CRITICAL
Official page ↗
- Status
- Modified
- Published
- 2026-07-01
- Last modified
- 2026-10-25
- Assigner
- 33c584b5-0579-4c06-b2a0-8d8329fcab9c
- CVSS 4.0 (33c584b5-0579-4c06-b2a0-8d8329fcab9c)
- 9.3 CRITICAL — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- CVSS 3.1 (33c584b5-0579-4c06-b2a0-8d8329fcab9c)
- 9.8 CRITICAL — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Weaknesses
- CWE-787
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.
Affected configurations
• uvnc ultravnc (<= 1.8.2.2)
Related
Weakness · CWE (1)
- CWE-787 Out-of-bounds Write weakness