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HIGH severity

CVE-2026-23953 — incus

HIGH

CVE-2026-23953 is a high-severity (CVSS 8.7) CWE-93 vulnerability in github.com/lxc/incus/v6. A fix is available for github.com/lxc/incus/v6 — see the affected versions and patch details below.

Incus container environment configuration newline injection

Also known asGHSA-x6jc-phwx-hp32GO-2026-4359
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
  • A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-23953.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs42th percentile — riskier than 42% of all scored CVEsHighest risk
0.00%0.33%0.67%1.00%0.0%0.5%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐹github.com/lxc/incus/v6

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Summary

A user with the ability to launch a container with a custom YAML configuration (e.g a member of the ‘incus’ group) can create an environment variable containing newlines, which can be used to add additional configuration items in the container’s lxc.conf due to the newline injection. This can allow adding arbitrary lifecycle hooks, ultimately resulting in arbitrary command execution on the host.

Details

When passing environment variables in the config block of a new container, values are not checked for the presence of newlines [1], which can result in newline injection inside the generated container lxc.conf. This can be used to set arbitrary additional configuration items, such as lxc.hook.pre-start. By exploiting this, a user with the ability to launch a container with an arbitrary config can achieve arbitrary command execution as root on the host.

Exploiting this issue on IncusOS requires a slight modification of the payload to change to a different writable directory for the validation step (e.g /tmp). This can be confirmed with a second container with /tmp mounted from the host (A privileged action for validation only).

[1] https://github.com/lxc/incus/blob/HEAD/internal/server/instance/drivers/driver_lxc.go#L1081

PoC

A proof-of-concept script exploiting this vulnerability can be found attached, named environment_newline_injection.sh, showing arbitrary command execution, which will write a file to the root filesystem (/newline_injection_command_exec_poc)

Manual Reproduction steps:

  1. Launch a new container with a configuration file containing a multiline YAML string as an environment variable value, such as in the listing below.
  2. Observe that the lxc.conf (/run/incus/user-1000_poc/lxc.conf in my case) contains an additional lxc.hook.pre-start item
  3. Observe the creation of the file in the host root directory, with contents proving command execution as root.
incus launch images:alpine/edge --ephemeral poc << EOF
config:
  environment.FOO: |-
    abc
    lxc.hook.pre-start = /bin/sh -c "id > /newline_injection_command_exec_poc"
EOF

Impact

A user with the ability to launch a container with a custom YAML configuration (e.g a member of the ‘incus’ group) can achieve arbitrary command execution on the host.

Attachments

environment_newline_injection.sh environment_newline_injection.patch

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/lxc/incus/v6all versions6.21.0go get github.com/lxc/incus/v6@v6.21.0

Affected Products

1 product · 2 configurations
Application
incuslinuxcontainers
≥ 6.1.0 && ≤ 6.0.5
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/lxc/incus/v6, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/lxc/incus/v6 to 6.21.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23953 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Summary A user with the ability to launch a container with a custom YAML configuration (e.g a member of the ‘incus’ group) can create an environment variable containing newlines, which can be used to add additional configuration items in the container’s `lxc.conf` due to the newline injection. This can allow adding arbitrary lifecycle hooks, ultimately resulting in arbitrary command execution on the host. ### Details When passing environment variables in the config block of a new container, values are not checked for the presence of newlines [1], which can result in newline injection insi
O3 Security · Impact-Aware SCA

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CVE-2026-23953: incus — Fixed in 6.21.0