What’s Vulnerable › Vulnerabilities

CVE-2026-7828: UltraVNC repeater integer overflow in win_log malloc leading to heap overflow

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-01 · updated 2026-10-25
• Weakness: CWE-190

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.

Affected products

• Kaspersky Lab UltraVNC: through 1.8.2.2

References

• https://github.com/ultravnc/UltraVNC
• https://uvnc.com/
• https://www.securin.io/zero-days/cve-2026-7828-integer-overflow-win-log-malloc-ultravnc-repeater

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