UBUNTU-CVE-2026-72854

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Source
https://ubuntu.com/security/CVE-2026-72854
Import Source
https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-72854.json
JSON Data
https://api.osv.dev/v1/vulns/UBUNTU-CVE-2026-72854
Upstream
Published
2026-08-20T19:17:00Z
Modified
2026-09-02T19:36:30Z
Severity
  • 5.3 (Medium) CVSS_V3 - CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:L CVSS Calculator
  • 5.8 (Medium) CVSS_V4 - CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N CVSS Calculator
  • Ubuntu - medium
Summary
[none]
Details

msgpack_unpacker_expand_buffer in src/unpack.c, reached through the public msgpack_unpacker_reserve_buffer API, computes its new buffer size using an unchecked size_t addition of the requested size and the amount already used. The doubling loop guards its own multiplication against overflow, but the addition in the loop condition is unguarded, so a request near SIZE_MAX wraps: the loop condition is already satisfied, the allocation is performed at the small pre-wrap size, and the function returns true. The caller is told the requested capacity was reserved when it was not, so a subsequent write of the requested length overflows the heap buffer. The library's own example/lib_buffer_unpack.c demonstrates the reserve-then-write pattern, and its defensive assert comparing capacity against the request is compiled out under NDEBUG. msgpack-c's own decode entry points do not derive the reservation size from untrusted input, so reaching this requires an integration that passes an attacker-influenced length to the reservation API, such as a length-prefixed streaming transport.

References

Affected packages

Ubuntu:18.04:LTS / msgpack-c

Package

Name
msgpack-c
Purl
pkg:deb/ubuntu/msgpack-c?arch=source&distro=bionic

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

2.*
2.1.5-1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "libmsgpackc2",
            "binary_version": "2.1.5-1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-72854.json"

Ubuntu:20.04:LTS / msgpack-c

Package

Name
msgpack-c
Purl
pkg:deb/ubuntu/msgpack-c?arch=source&distro=focal

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

3.*
3.0.1-3

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "libmsgpackc2",
            "binary_version": "3.0.1-3"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-72854.json"

Ubuntu:22.04:LTS / msgpack-c

Package

Name
msgpack-c
Purl
pkg:deb/ubuntu/msgpack-c?arch=source&distro=jammy

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

3.*
3.3.0-4

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "libmsgpackc2",
            "binary_version": "3.3.0-4"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-72854.json"

Ubuntu:24.04:LTS / msgpack-c

Package

Name
msgpack-c
Purl
pkg:deb/ubuntu/msgpack-c?arch=source&distro=noble

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

4.*
4.0.0-3
4.0.0-3build1

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "libmsgpackc2",
            "binary_version": "4.0.0-3build1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-72854.json"

Ubuntu:26.04:LTS / msgpack-c

Package

Name
msgpack-c
Purl
pkg:deb/ubuntu/msgpack-c?arch=source&distro=resolute

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0 Unknown introduced version / All previous versions are affected

Affected versions

6.*
6.0.1-3
6.1.0-2

Ecosystem specific 

{
    "binaries": [
        {
            "binary_name": "libmsgpack-c2",
            "binary_version": "6.1.0-2"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-72854.json"