Security readout for executives and security teams
Plain-English summary
Rancher versions before 2.5.9 and 2.4.16 could let an authenticated cluster user make Rancher treat them as another user or group. That can turn limited access into broad control inside affected clusters, threatening confidentiality, integrity, and availability.
Executive priority
Treat this as a high-priority remediation for affected Rancher environments. A compromised or malicious cluster user could potentially gain another user’s authority, creating material risk to production Kubernetes control, sensitive data, and service availability.
Technical view
The CVE describes CWE-807 reliance on untrusted input in a security decision. Rancher accepted forged impersonation-related headers, including Impersonate-User or Impersonate-Group, allowing cluster users to act as other users. The listed CVSS is 8.8, network reachable, low complexity, and requires low privileges.
Likely exposure
Exposure is most likely where Rancher instances run versions prior to 2.5.9 or prior to 2.4.16 and have users with cluster access. The bundle does not identify specific deployment modes, managed offerings, or default configurations beyond affected Rancher versions.
Exploitation context
The provided sources do not show CISA KEV listing or confirmed active exploitation. The weakness requires a user already in the cluster, but no user interaction and low attack complexity are reported, so insider, compromised-account, or tenant-to-tenant escalation scenarios matter.
Researcher notes
Evidence is limited to the CVE description and SUSE Bugzilla reference in the bundle. The affected-version statement supports upgrade-based remediation, but the bundle does not provide exploit traces, detailed vulnerable code paths, or operational detection rules.
Mitigation direction
- Upgrade Rancher beyond the affected 2.5.x and 2.4.x version ranges.
- Check Rancher or SUSE guidance for version-specific remediation details.
- Restrict Rancher and cluster access to necessary, trusted users only.
- Review high-privilege cluster roles and remove unnecessary assignments.
Validation and detection
- Inventory all Rancher instances and record exact versions.
- Flag any Rancher version older than 2.5.9 or 2.4.16.
- Confirm upgrade status through package, container, or deployment metadata.
- Review audit logs for unexpected impersonation or identity changes.
- Validate RBAC still matches intended user responsibilities after remediation.
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-807: 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 lookupPrivilege behavior lookup
The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-31999 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
- 8.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/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:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H2.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://bugzilla.suse.com/show_bug.cgi?id=1187084CVE reference · x_refsource_CONFIRM
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.
Reliance on Untrusted Inputs in a Security Decision
Reliance on Untrusted Inputs in a Security Decision represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.