CVE-2026-7828
UltraVNC repeater integer overflow in win_log malloc leading to heap overflow
Description
UltraVNC repeater through 1.8.2.2 contains an integer overflow in the HTTP request logging path. In repeater/webgui/settings.c:336, the win_log() function allocates list nodes via malloc(sizeof(struct LIST) + strlen(line)), where line is derived from HTTP request URIs. If strlen(line) is sufficiently large, the addition overflows to a value smaller than sizeof(struct LIST), causing a heap allocation smaller than required. The subsequent strcpy of the full string into the undersized allocation produces a heap buffer overflow. In the current implementation this overflow is bounded by the HTTP receive buffer size (WI_RXBUFSIZE = 153600 bytes, well below SIZE_MAX on 32-bit builds), limiting practical exploitability to a partial heap write. A remote unauthenticated attacker can trigger the theoretical overflow path by sending a maximally-sized URI in an HTTP request to the repeater HTTP port.
INFO
Published Date :
July 1, 2026, 3:33 a.m.
Last Modified :
July 1, 2026, 3:33 a.m.
Remotely Exploit :
Yes !
Source :
securin
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | 33c584b5-0579-4c06-b2a0-8d8329fcab9c |
Solution
- Update UltraVNC repeater to version 1.8.2.2 or later.
- Apply vendor patches for integer overflow and heap buffer overflow.
- Restrict access to the repeater HTTP port.
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