---
title: "CVE-2026-12249: Canonical ADSys Uses a Less Trusted Source"
url: https://erroneo.us/security/cve/CVE-2026-12249/
description: "CVE-2026-12249 (github.com/ubuntu/adsys (Go)): An issue was discovered in Canonical ADSys upstream versions through v0.16.2. During Active Directory…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-06-22
date_modified: 2026-09-21
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-12249"
kev: false
cvss: 9
epss: 0.00143
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-12249: Canonical ADSys Uses a Less Trusted Source

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.1% , percentile 3: FIRST’s model estimates a 0.1% chance of exploitation activity in the next 30 days, higher than 3% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes github.com/ubuntu/adsys (Go) < 0.16.3-0.20250318112551-8b1939f96d38, fixed in 0.16.3-0.20250318112551-8b1939f96d38 . Check your lockfile, including transitive dependencies.

## What it is

An issue was discovered in Canonical ADSys upstream versions through v0.16.2. During Active Directory Certificate Services (AD CS) certificate auto-enrollment via the vendored Samba client script (internal/policies/certificate/python/vendorsamba/gp/gpcertautoenrollext.py), ADSys utilizes a plaintext HTTP connection (http://) instead of a secure HTTPS connection (https://) to request the CA certificate from the Active Directory Certificate Services server (GetCACert). An unauthenticated network attacker positioned between the managed Ubuntu host and the configured AD CS CA hostname can conduct a Man-in-the-Middle (MITM) attack. By intercepting the plaintext HTTP request, the attacker can supply an arbitrary, attacker-controlled Root CA certificate. Because the system automatically accepts this certificate and registers it into the local system trust store via update-ca-certificates, this results in system-wide trust store poisoning. Consequently, TLS clients utilizing the operating system trust store on the affected machine will accept rogue certificates for arbitrary domains, enabling persistent decryption and interception of subsequent TLS connections. This issue is resolved in version v0.16.3.

## Affected packages

- Go `github.com/ubuntu/adsys` < 0.16.3-0.20250318112551-8b1939f96d38 → fixed: 0.16.3-0.20250318112551-8b1939f96d38

## Affected products (CVE record)

-  adsys: 0.13.0 < 0.16.3
- Canonical Ubuntu 20.04 LTS: see advisory
- Canonical Ubuntu 22.04 LTS: see advisory
- Canonical Ubuntu 24.04 LTS: see advisory
- Canonical Ubuntu 25.10: see advisory
- Canonical Ubuntu 26.04 LTS: see advisory

## Severity

- canonical CVSS 3.1: 8.3 `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H`
- canonical CVSS 4.0: 9 `CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:P/S:N/AU:Y/R:I/V:D/RE:L/U:Red`
- GitHub CVSS 4.0: 9.0 `CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:P/S:N/AU:Y/R:I/V:D/RE:L/U:Red`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.14% probability of exploitation activity in the next 30 days; percentile 3.

## Sources

- [github.com](https://github.com/ubuntu/adsys/commit/8b1939f96d3827b4426eb06c1ced5bf317b0a99d)
- [GitHub Advisory GHSA-crm4-q7v4-c2r2](https://github.com/advisories/GHSA-crm4-q7v4-c2r2)
- [CVE.org record CVE-2026-12249](https://www.cve.org/CVERecord?id=CVE-2026-12249)
- [NVD entry CVE-2026-12249](https://nvd.nist.gov/vuln/detail/CVE-2026-12249)
- [ubuntu.com](https://ubuntu.com/security/CVE-2026-12249)
- [github.com](https://github.com/ubuntu/adsys/releases/tag/v0.16.3)

---
Source page: https://erroneo.us/security/cve/CVE-2026-12249/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt