What is CVE-2026-7840?

CVE-2026-7840 is a critical-severity vulnerability in Uvnc Ultravnc, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-07-01.

How severe is CVE-2026-7840?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Uvnc Ultravnc

CVE-2026-7840

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 fi…

Vulnerability class: Buffer Overflow

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

Affected products

Uvnc Ultravnc — versions 0

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

References

33c584b5-0579-4c06-b2a0-8d8329fcab9c (vendor-advisory)
33c584b5-0579-4c06-b2a0-8d8329fcab9c (product)

Frequently asked questions

What is CVE-2026-7840?: CVE-2026-7840 is a critical-severity vulnerability in Uvnc Ultravnc, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2026-07-01.
How severe is CVE-2026-7840?: Critical severity. CVSS v3 base score is 9.8 out of 10.