Out-of-bounds read in LibVNCServer - CVE-2026-32853
Published: April 27, 2026
Vulnerability identifier: #VU128150
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-32853
CWE-ID: CWE-125
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: LibVNC
Affected software:
LibVNCServer
LibVNCServer
Detailed vulnerability description
The vulnerability allows a remote attacker to disclose sensitive information or cause a denial of service.
The vulnerability exists due to out-of-bounds read in the HandleUltraZipBPP function in src/libvncclient/ultra.c when processing UltraZip-encoded FramebufferUpdate messages. A remote attacker can send a specially crafted FramebufferUpdate message with an attacker-controlled subrectangle count to disclose sensitive information or cause a denial of service.
UltraZip encoding is enabled by default in LibVNCClient, and no authentication is required on the server side when using rfbSecTypeNone.
How to mitigate CVE-2026-32853
Install security update from vendor's website.