Ubuntu 20.04 LTS: Use of Less Trusted Source
CVE-2026-12249 is a critical-severity use of less trusted source vulnerability in Ubuntu 20.04 LTS from Canonical, with a CVSS 3.1 base score of 9.0 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. There is no confirmed exploitation so far. EPSS estimates a 0.14% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Check which version of Ubuntu 20.04 LTS you run against the affected versions below, and install the vendor's latest release.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Canonical | Ubuntu 20.04 LTS | Not specified in the record | Not stated |
| Canonical | Ubuntu 22.04 LTS | Not specified in the record | Not stated |
| Canonical | Ubuntu 24.04 LTS | Not specified in the record | Not stated |
| Canonical | Ubuntu 25.10 | Not specified in the record | Not stated |
| Canonical | Ubuntu 26.04 LTS | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (ubuntu.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 9.0 | Critical | CNA (ubuntu.com) |
| CVSS 3.1 | 9.0 | Critical | CNA (ubuntu.com) |
Official description
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/vendor_samba/gp/gp_cert_auto_enroll_ext.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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use of Less Trusted Source
The product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
References
Patches and release notes
Other references
Other vulnerabilities in Ubuntu 20.04 LTS
- 8.4 High severity
- 9.0 Critical severity
- 7.8 High severity
Recent Use of Less Trusted Source vulnerabilities
- 10.0 Critical severity
- 7.5 High severity
- 7.5 High severity
- 8.8 High severity
- 8.2 High severity
- 7.1 High severity
Spotted an error? Tell us.