Vulnerability Description
UltraVNC repeater through 1.8.2.2 contains a post-authentication out-of-bounds write in the allow/deny rule parser. In repeater/webgui/settings.c:225-272, after strncpy_s copies a rule token into temp1[rule1] (25-byte destination) or temp2/temp3 (16-byte destination), the code unconditionally writes a NUL terminator at temp1[rule1][len] = 0 without clamping len to the destination size. When an authenticated administrator saves a rule with a token length equal to or greater than the destination size, the NUL byte is written one or more bytes past the end of the stack-allocated array, corrupting adjacent stack data. An attacker who has obtained admin credentials (including via CVE-2026-7839 default password) can trigger this to gain code execution on the repeater host.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Uvnc | Ultravnc | <= 1.8.2.2 |
Related Weaknesses (CWE)
References
- https://github.com/ultravnc/UltraVNCProduct
- https://uvnc.com/ProductRelease Notes
- https://www.securin.io/zero-days/cve-2026-7829-post-auth-oob-nul-write-repeater-
FAQ
What is CVE-2026-7829?
CVE-2026-7829 is a vulnerability with a CVSS score of 7.2 (HIGH). UltraVNC repeater through 1.8.2.2 contains a post-authentication out-of-bounds write in the allow/deny rule parser. In repeater/webgui/settings.c:225-272, after strncpy_s copies a rule token into temp...
How severe is CVE-2026-7829?
CVE-2026-7829 has been rated HIGH with a CVSS base score of 7.2/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-7829?
Check the references section above for vendor advisories and patch information. Affected products include: Uvnc Ultravnc.