libvncserver — security advisory
LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, 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. It needs no authentication (the attacker is the server), works in a default build with default settings, and fires from a single `FramebufferUpdate` the moment the victim connects. It crashes any client unconditionally (denial of service); we also demonstrated it overwriting an application callback pointer and redirecting execution to attacker-chosen code (code execution) under the default configuration. Commit 540332be3e0acc566fa64da6f1b4680c72c724dd patches the issue.
- Products
- libvncserver
- Affected versions
- 0.9.14+dfsg-1, 0.9.14+dfsg-1+deb12u1, 0.9.15+dfsg-1, 0.9.15+dfsg-1+deb13u1, 0.9.15+dfsg-2, 0.9.15+dfsg-3, 0.9.15+dfsg-4, 0.9.15+dfsg-5
- Fixed versions
- 0.9.14+dfsg-1+deb12u2, 0.9.15+dfsg-1+deb13u2, 0.9.15+dfsg-6
- CVEs
- CVE-2026-50538
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 30 Oct 2026, 09:03 UTC · Revision 1
Source evidence
LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, 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. It needs no authentication (the attacker is the server), works in a default build with default settings, and fires from a single `FramebufferUpdate` the moment the victim connects. It crashes any client unconditionally (denial of service); we also demonstrated it overwriting an application callback pointer and redirecting execution to attacker-chosen code (code execution) under the default configuration. Commit 540332be3e0acc566fa64da6f1b4680c72c724dd patches the issue.
osv:DEBIAN-CVE-2026-50538
libvncserver
Fixed versions: 0.9.14+dfsg-1+deb12u2
libvncserver
Fixed versions: 0.9.15+dfsg-1+deb13u2
libvncserver
Fixed versions: 0.9.15+dfsg-6
Complete source record
{
"id": "efec993a9d71abcae40f6a270dab772e9211b5c3b8c198f2d151d6cdf0a363e4",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-50538",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "DEBIAN-CVE-2026-50538",
"summary": "LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, 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. It needs no authentication (the attacker is the server), works in a default build with default settings, and fires from a single `FramebufferUpdate` the moment the victim connects. It crashes any client unconditionally (denial of service); we also demonstrated it overwriting an application callback pointer and redirecting execution to attacker-chosen code (code execution) under the default configuration. Commit 540332be3e0acc566fa64da6f1b4680c72c724dd patches the issue.",
"evidence": "osv:DEBIAN-CVE-2026-50538",
"products": [
{
"name": {
"value": "libvncserver",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "0.9.14+dfsg-1+deb12u2",
"evidence": "/affected/0/ranges"
}
],
"affected_versions": [
{
"value": "0.9.14+dfsg-1",
"evidence": "/affected/0/versions"
},
{
"value": "0.9.14+dfsg-1+deb12u1",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "libvncserver",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "0.9.15+dfsg-1+deb13u2",
"evidence": "/affected/1/ranges"
}
],
"affected_versions": [
{
"value": "0.9.15+dfsg-1",
"evidence": "/affected/1/versions"
},
{
"value": "0.9.15+dfsg-1+deb13u1",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "libvncserver",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [
{
"value": "0.9.15+dfsg-6",
"evidence": "/affected/2/ranges"
}
],
"affected_versions": [
{
"value": "0.9.15+dfsg-1",
"evidence": "/affected/2/versions"
},
{
"value": "0.9.15+dfsg-2",
"evidence": "/affected/2/versions"
},
{
"value": "0.9.15+dfsg-3",
"evidence": "/affected/2/versions"
},
{
"value": "0.9.15+dfsg-4",
"evidence": "/affected/2/versions"
},
{
"value": "0.9.15+dfsg-5",
"evidence": "/affected/2/versions"
}
]
}
],
"severity": "high",
"structured": {
"id": "DEBIAN-CVE-2026-50538",
"aliases": [
"DEBIAN-CVE-2026-50538"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "0.9.14+dfsg-1+deb12u2"
}
]
}
],
"package": {
"name": "libvncserver",
"purl": "pkg:deb/debian/libvncserver?arch=source&distro=bookworm",
"ecosystem": "Debian:12"
},
"versions": [
"0.9.14+dfsg-1",
"0.9.14+dfsg-1+deb12u1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-50538.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "0.9.15+dfsg-1+deb13u2"
}
]
}
],
"package": {
"name": "libvncserver",
"purl": "pkg:deb/debian/libvncserver?arch=source&distro=trixie",
"ecosystem": "Debian:13"
},
"versions": [
"0.9.15+dfsg-1",
"0.9.15+dfsg-1+deb13u1"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-50538.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
},
{
"fixed": "0.9.15+dfsg-6"
}
]
}
],
"package": {
"name": "libvncserver",
"purl": "pkg:deb/debian/libvncserver?arch=source&distro=forky",
"ecosystem": "Debian:14"
},
"versions": [
"0.9.15+dfsg-1",
"0.9.15+dfsg-2",
"0.9.15+dfsg-3",
"0.9.15+dfsg-4",
"0.9.15+dfsg-5"
],
"database_specific": {
"source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-50538.json"
},
"ecosystem_specific": {
"urgency": "not yet assigned"
}
}
],
"modified": "2026-10-13T09:47:41.803429028Z",
"provider": "osv",
"upstream": [
"CVE-2026-50538"
],
"references": [
"https://security-tracker.debian.org/tracker/CVE-2026-50538"
]
},
"related_cves": [
{
"value": "CVE-2026-50538",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 307588,
"published_at": "2026-08-21T21:16:59.807+00:00"
}