UBUNTU-CVE-2026-59679
fs_read_glyphs() in the libXfont2 font-server client (src/fc/fserve.c) indexes the per-character encoding[] array using num_chars from the FS_QueryXBitmaps16 reply, but that array was allocated with a size derived from num_extents in the separate FS_QueryXExtents16 reply. The two CARD32 fields are never cross-checked. A malicious or compromised font server can send a small num_extents (e.g. 1) in the extents reply, then a large num_chars (e.g. 100000) in the bitmaps reply. This causes attacker-controlled out-of-bounds heap read and writes.
UBUNTU-CVE-2026-59679
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: osv:UBUNTU-CVE-2026-59679
libxfont2
Source reference: /affected/0/package/name
- Affected versions
- 1:2.0.1-3~ubuntu16.04.1
Source reference:
/affected/0/versions1:2.0.1-3~ubuntu16.04.2Source reference:
/affected/0/versions1:2.0.1-3~ubuntu16.04.3Source reference:
/affected/0/versions - Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "libxfont2",
"purl": "pkg:deb/ubuntu/libxfont2?arch=source&distro=xenial",
"ecosystem": "Ubuntu:16.04:LTS"
},
"versions": [
"1:2.0.1-3~ubuntu16.04.1",
"1:2.0.1-3~ubuntu16.04.2",
"1:2.0.1-3~ubuntu16.04.3"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-59679.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libxfont2",
"binary_version": "1:2.0.1-3~ubuntu16.04.3"
}
]
}
}
]Publisher severity
No explicit severity was provided.
- Event
- #23440 · Revision 1
- Added to Heist Feed
- Publisher date