CVE-2026-7828 UltraVNC repeater integer overflow in win_log malloc leading to heap overflow
A remote unauthenticated attacker can trigger a heap buffer overflow via integer overflow in HTTP logging, potentially causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-7828?
CVE-2026-7828 is a medium-severity vulnerability in uvnc UltraVNC, published on 1 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-190
Which versions are affected by CVE-2026-7828?
It affects 1 product.
Products include Uvnc Ultravnc.
How do I fix CVE-2026-7828?
No fix has been published for CVE-2026-7828 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-7828 being exploited?
There is no known exploitation of CVE-2026-7828 in the wild and no public exploit code.
Other vulnerabilities in uvnc UltraVNC
Sources
Also known as GHSA-hpq9-2mqh-7fg9.