Security readout for executives and security teams
Plain-English summary
CVE-2021-3899 is a local privilege escalation issue in Canonical Apport. A logged-in attacker could exploit a race condition in executable replacement checks to run code as root, but the source bundle notes this depends on the correct local configuration.
Executive priority
Treat this as high priority for Ubuntu fleets with shared or less-trusted local access. It is not described as remotely exploitable, but successful exploitation could give root-level control on an affected host.
Technical view
The vulnerability is a CWE-367 time-of-check/time-of-use race in Apport's 'replaced executable' detection. CVSS 3.1 is 7.8 with local attack vector, low complexity, low privileges required, no user interaction, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is most relevant to Ubuntu systems using the Apport package, especially multi-user systems or environments where less-trusted users can get local access. The bundle does not provide exact affected or fixed package versions.
Exploitation context
The source bundle does not show CISA KEV listing or other evidence of active exploitation. Exploitation is local, requires low privileges, and depends on local configuration, so internet-facing exposure is not the primary risk.
Researcher notes
Evidence supports a local TOCTOU privilege escalation in Apport. The bundle identifies Canonical Apport and USN-5427-1, but does not include fixed version details, affected Ubuntu release mapping, exploit proof, or confirmed exploitation status.
Mitigation direction
- Review Ubuntu USN-5427-1 for affected releases and fixed Apport packages.
- Apply Canonical or Ubuntu Apport updates through normal OS patch management.
- Prioritize multi-user Ubuntu hosts and systems with less-trusted local accounts.
- If fix status is unknown, treat Apport-enabled Ubuntu systems as exposed until verified.
Validation and detection
- Inventory Ubuntu systems with the apport package installed.
- Compare installed Apport package versions against Ubuntu USN-5427-1 guidance.
- Confirm vulnerable systems have received the vendor security update.
- Review local account exposure on systems where Apport is present.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-367: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-3899 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H1.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://bugs.launchpad.net/ubuntu/+source/apport/+bug/1948376CVE reference · issue-tracking
- https://ubuntu.com/security/notices/USN-5427-1CVE reference · vendor-advisory
- https://www.cve.org/CVERecord?id=CVE-2021-3899CVE reference · issue-tracking
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Time-of-check Time-of-use (TOCTOU) Race Condition
Time-of-check Time-of-use (TOCTOU) Race Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.