UBUNTU-CVE-2026-19742

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Source
https://ubuntu.com/security/CVE-2026-19742
Import Source
https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-19742.json
JSON Data
https://api.osv.dev/v1/vulns/UBUNTU-CVE-2026-19742
Upstream
Published
2026-10-26T17:17:00Z
Modified
2026-10-28T20:16:02Z
Severity
  • 3.7 (Low) CVSS_V3 - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N CVSS Calculator
  • 3.7 (Low) CVSS_V3 - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N CVSS Calculator
  • Ubuntu - medium
Summary
[none]
Details

The IPv6 stack derived the long-lived secret key used to compute RFC 7217 stable interface identifiers (gen_stable_iid() in subsys/net/ip/ipv6.c) and RFC 8981 temporary interface identifiers (gen_temporary_iid() in subsys/net/ip/ipv6_pe.c) with sys_rand_get(). That API is documented as not cryptographically secure, while both RFCs require this key to be an unpredictable random value of at least 128 bits — the unpredictability of every generated IID rests entirely on it. Depending on the platform, sys_rand_get() resolves either to a hardware entropy device or, on boards whose entropy driver sets CONFIG_ENTROPY_NEEDS_PRNG, to the non-cryptographic xoshiro128++ generator in subsys/random/random_xoshiro128.c, which keeps a single global 128-bit state shared with every other sys_rand_get() consumer. Many of those consumers put their output directly on the wire (ephemeral source ports, DNS query IDs, CoAP message IDs and tokens, DHCPv6 transaction IDs, WebSocket masking keys), and the xoshiro state transition is invertible, so an observer of a device's traffic can recover the generator state and reconstruct the IID secret key. Additionally, with the entropy-device backend sys_rand_get() silently falls back to k_cycle_get_32() samples when the entropy driver fails, and returns no error, so the key could be derived from the cycle counter without the caller noticing. With the key known, stable IIDs become directly computable for any prefix (the remaining HMAC inputs — prefix, interface index, interface name, DAD counter — are guessable), and temporary IIDs become linkable after a cheap search over the mixed-in k_uptime_get_32() value. This defeats the properties both features exist to provide: an attacker can track a device across networks and prefixes, and can predict its address inside a /64 without scanning, removing the usual barrier to directly targeting the host. There is no memory-safety, integrity, or availability impact. The fix generates the key with sys_csrand_get() and aborts IID generation with -EIO when no cryptographic randomness is available, instead of silently deriving addresses from a predictable key. Both CONFIG_NET_IPV6_IID_STABLE and CONFIG_NET_IPV6_PE are experimental and disabled by default; builds using CONFIG_TEST_RANDOM_GENERATOR remain predictable by design, as sys_csrand_get() is deliberately routed back to the test generator there.

References

Affected packages

Ubuntu:16.04:LTS
zephyr

Package

Name
zephyr
Purl
pkg:deb/ubuntu/zephyr?arch=source&distro=xenial

Affected ranges

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

Affected versions

3.*
3.1.2-1
3.1.2-1build1

Ecosystem specific 

{
    "binaries":  [
        {
            "binary_name":  "libzephyr4",
            "binary_version":  "3.1.2-1build1"
        },
        {
            "binary_name":  "libzephyr4-krb5",
            "binary_version":  "3.1.2-1build1"
        },
        {
            "binary_name":  "zephyr-clients",
            "binary_version":  "3.1.2-1build1"
        },
        {
            "binary_name":  "zephyr-server",
            "binary_version":  "3.1.2-1build1"
        },
        {
            "binary_name":  "zephyr-server-krb5",
            "binary_version":  "3.1.2-1build1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-19742.json"
Ubuntu:18.04:LTS
zephyr

Package

Name
zephyr
Purl
pkg:deb/ubuntu/zephyr?arch=source&distro=bionic

Affected ranges

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

Affected versions

3.*
3.1.2-1build1
3.1.2-1build2

Ecosystem specific 

{
    "binaries":  [
        {
            "binary_name":  "libzephyr4",
            "binary_version":  "3.1.2-1build2"
        },
        {
            "binary_name":  "libzephyr4-krb5",
            "binary_version":  "3.1.2-1build2"
        },
        {
            "binary_name":  "zephyr-clients",
            "binary_version":  "3.1.2-1build2"
        },
        {
            "binary_name":  "zephyr-server",
            "binary_version":  "3.1.2-1build2"
        },
        {
            "binary_name":  "zephyr-server-krb5",
            "binary_version":  "3.1.2-1build2"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-19742.json"
Ubuntu:20.04:LTS
zephyr

Package

Name
zephyr
Purl
pkg:deb/ubuntu/zephyr?arch=source&distro=focal

Affected ranges

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

Affected versions

3.*
3.1.2-1build3

Ecosystem specific 

{
    "binaries":  [
        {
            "binary_name":  "libzephyr4",
            "binary_version":  "3.1.2-1build3"
        },
        {
            "binary_name":  "libzephyr4-krb5",
            "binary_version":  "3.1.2-1build3"
        },
        {
            "binary_name":  "zephyr-clients",
            "binary_version":  "3.1.2-1build3"
        },
        {
            "binary_name":  "zephyr-server",
            "binary_version":  "3.1.2-1build3"
        },
        {
            "binary_name":  "zephyr-server-krb5",
            "binary_version":  "3.1.2-1build3"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-19742.json"
Ubuntu:22.04:LTS
zephyr

Package

Name
zephyr
Purl
pkg:deb/ubuntu/zephyr?arch=source&distro=jammy

Affected ranges

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

Affected versions

3.*
3.1.2-1build3

Ecosystem specific 

{
    "binaries":  [
        {
            "binary_name":  "libzephyr4",
            "binary_version":  "3.1.2-1build3"
        },
        {
            "binary_name":  "libzephyr4-krb5",
            "binary_version":  "3.1.2-1build3"
        },
        {
            "binary_name":  "zephyr-clients",
            "binary_version":  "3.1.2-1build3"
        },
        {
            "binary_name":  "zephyr-server",
            "binary_version":  "3.1.2-1build3"
        },
        {
            "binary_name":  "zephyr-server-krb5",
            "binary_version":  "3.1.2-1build3"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-19742.json"
Ubuntu:24.04:LTS
zephyr

Package

Name
zephyr
Purl
pkg:deb/ubuntu/zephyr?arch=source&distro=noble

Affected ranges

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

Affected versions

3.*
3.1.2-1.1
3.1.2-1.1build1

Ecosystem specific 

{
    "binaries":  [
        {
            "binary_name":  "libzephyr4",
            "binary_version":  "3.1.2-1.1build1"
        },
        {
            "binary_name":  "libzephyr4-krb5",
            "binary_version":  "3.1.2-1.1build1"
        },
        {
            "binary_name":  "zephyr-clients",
            "binary_version":  "3.1.2-1.1build1"
        },
        {
            "binary_name":  "zephyr-server",
            "binary_version":  "3.1.2-1.1build1"
        },
        {
            "binary_name":  "zephyr-server-krb5",
            "binary_version":  "3.1.2-1.1build1"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-19742.json"
Ubuntu:26.04:LTS
zephyr

Package

Name
zephyr
Purl
pkg:deb/ubuntu/zephyr?arch=source&distro=resolute

Affected ranges

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

Affected versions

3.*
3.1.2-1.1build1
3.1.2-4

Ecosystem specific 

{
    "binaries":  [
        {
            "binary_name":  "libzephyr4",
            "binary_version":  "3.1.2-4"
        },
        {
            "binary_name":  "libzephyr4-krb5",
            "binary_version":  "3.1.2-4"
        },
        {
            "binary_name":  "zephyr-clients",
            "binary_version":  "3.1.2-4"
        },
        {
            "binary_name":  "zephyr-server",
            "binary_version":  "3.1.2-4"
        },
        {
            "binary_name":  "zephyr-server-krb5",
            "binary_version":  "3.1.2-4"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-19742.json"
Ubuntu:26.10
zephyr

Package

Name
zephyr
Purl
pkg:deb/ubuntu/zephyr?arch=source&distro=stonking

Affected ranges

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

Affected versions

3.*
3.1.2-4

Ecosystem specific 

{
    "binaries":  [
        {
            "binary_name":  "libzephyr4",
            "binary_version":  "3.1.2-4"
        },
        {
            "binary_name":  "libzephyr4-krb5",
            "binary_version":  "3.1.2-4"
        },
        {
            "binary_name":  "zephyr-clients",
            "binary_version":  "3.1.2-4"
        },
        {
            "binary_name":  "zephyr-server",
            "binary_version":  "3.1.2-4"
        },
        {
            "binary_name":  "zephyr-server-krb5",
            "binary_version":  "3.1.2-4"
        }
    ]
}

Database specific

source 
"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-19742.json"