Ubuntu Kernel: Incorrect Authorization
CVE-2023-2640 is a high-severity incorrect authorization vulnerability in Ubuntu Kernel from Canonical, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. There is no confirmed exploitation so far. EPSS estimates a 15.2% chance of exploitation within 30 days, which is in the top 3.19% of all scored CVEs.
EPSS places it among the vulnerabilities most likely to be exploited soon.
What to do
- Update ubantu_kernel to 6.2.0-26.26 or 6.0.0-1020.20 or 5.4.0-155.172, whichever matches your release line, or a later version.
- Read the advisory on ubuntu.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Canonical | Ubuntu Kernel | Not specified in the record | Not stated |
| Canonical | ubantu_kernel | before 6.2.0-26.26; before 6.0.0-1020.20; before 5.4.0-155.172 | 6.2.0-26.26, 6.0.0-1020.20, 5.4.0-155.172 |
| Canonical | Ubuntu Linux | 23.04 | 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
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- 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:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.8 | High | CNA (ubuntu.com) |
| CVSS 3.1 | 7.8 | High | NVD |
Official description
On Ubuntu kernels carrying both c914c0e27eb0 and "UBUNTU: SAUCE: overlayfs: Skip permission checking for trusted.overlayfs.* xattrs", an unprivileged user may set privileged extended attributes on the mounted files, leading them to be set on the upper files without the appropriate security checks.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Incorrect Authorization
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
How developers prevent this class of flaw
- Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries. Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Ensure that access control checks are performed related to the business logic. These checks may be different than the access control checks that are applied to more generic resources such as files, connections, processes, memory, and database records. For example, a database may restrict access for medical records to a specific database user, but each record might only be intended to be accessible to the patient and the patient's doctor.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using authorization frameworks such as the JAAS Authorization Framework and the OWASP ESAPI Access Control feature.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Patches and release notes
- lists.ubuntu.com/archives/kernel-team/2023-July/140923.htmlMailing List
- wiz.io/blog/ubuntu-overlayfs-vulnerabilityExploit, Mitigation, Third Party Advisory
Third-party and government advisories
- cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-2640Third Party Advisory
Other vulnerabilities in Ubuntu Kernel
- 7.8 High severity
Recent Incorrect Authorization vulnerabilities
- 7.5 High severity
- 7.2 High severity
- 8.8 High severity
- 9.8 Critical severity
- 7.8 High severity
- 7.8 High severity
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