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Debian LTS Advisory DLA-4755-1 [email protected]
https://www.debian.org/lts/security/ Abhijith PA
August 25, 2026 https://wiki.debian.org/LTS
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Package : libvncserver
Version : 0.9.13+dfsg-2+deb11u2
CVE ID : CVE-2026-32853 CVE-2026-32854 CVE-2026-44988 CVE-2026-50538
Debian Bug : 1132016 1132017 1138174 1138253
Several vulnerabilities were discovered in libvncserver, a
cross-platform library to implement VNC server or client functionality
in program
CVE-2026-32853
a heap out-of-bounds read vulnerability in the UltraZip encoding
handler that allows a malicious VNC server to cause information
disclosure or application crash. Attackers can exploit improper
bounds checking in the HandleUltraZipBPP() function by
manipulating subrectangle header counts to read beyond the
allocated heap buffer
CVE-2026-32854
null pointer dereference vulnerabilities in the HTTP proxy
handlers within httpProcessInput() in httpd.c that allow remote
attackers to cause a denial of service by sending specially
crafted HTTP requests. Attackers can exploit missing validation of
strchr() return values in the CONNECT and GET proxy handling paths
to trigger null pointer dereferences and crash the server when
httpd and proxy features are enabled.
CVE-2026-44988
LibVNCClient Tight Gradient decoding allows malicious
server-triggered heap/stack out-of-bounds writes
CVE-2026-50538
a malicious (or man-in-the-middle) VNC server can force a
connecting `libvncclient` to write attacker-controlled data past
the end of its framebuffer. This is an out-of-bounds heap write
with attacker-controlled length, contents, and offset.
For Debian 11 bullseye, these problems have been fixed in version
0.9.13+dfsg-2+deb11u2.
We recommend that you upgrade your libvncserver packages.
For the detailed security status of libvncserver please refer to
its security tracker page at:
https://security-tracker.debian.org/tracker/libvncserver
Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://wiki.debian.org/LTS
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