Security readout for executives and security teams
Plain-English summary
CVE-2021-25748 affects Kubernetes ingress-nginx. A user who can create or update Ingress objects could abuse a newline in an Ingress path to bypass sanitization and obtain the ingress-nginx controller credentials. In default configuration, those credentials can access all cluster secrets, making this a serious cluster confidentiality risk.
Executive priority
Treat this as high priority for shared or multi-team Kubernetes clusters. The business concern is not website defacement; it is possible exposure of cluster secrets after compromise of a lower-privileged Ingress authoring role.
Technical view
The flaw is improper input validation in ingress-nginx path handling. Sanitization of `spec.rules[].http.paths[].path` can be bypassed with a newline character in Ingress resources from `networking.k8s.io` or `extensions`. Successful abuse can expose the controller credential, which the source states has default access to all cluster secrets.
Likely exposure
Exposure is most likely in Kubernetes clusters using ingress-nginx where tenants, developers, CI systems, or operators can create or update Ingress objects. Risk is higher if the controller runs with broad secret-reading permissions, especially the default described in the CVE source.
Exploitation context
The source does not indicate known active exploitation, and the CVE is not listed as KEV. Exploitation requires authenticated Kubernetes permissions to create or update Ingress objects, but no user interaction is required once that access exists.
Researcher notes
Evidence in the provided bundle does not specify affected or fixed ingress-nginx versions. The key validation path is authorization and credential scope: who can write Ingress objects, and what the controller credential can access if exposed.
Mitigation direction
- Review vendor security guidance for affected ingress-nginx versions and fixes.
- Upgrade ingress-nginx if vendor guidance identifies a patched release.
- Restrict who can create or update Kubernetes Ingress objects.
- Apply least-privilege RBAC to the ingress-nginx controller service account.
- Review cluster secret access granted to ingress-related service accounts.
Validation and detection
- Inventory clusters running Kubernetes ingress-nginx.
- Audit RBAC subjects with create or update permissions on Ingress resources.
- Check whether ingress-nginx controller credentials can read secrets cluster-wide.
- Review existing Ingress path values for newline or unusual control characters.
- Confirm remediation status against Kubernetes ingress-nginx advisory guidance.
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
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ATT&CK lookup starting points
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CWE-20: Exact CWE lookup
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Open ATT&CK lookupCredential and access behavior lookup
The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupContainer behavior lookup
The affected technology mentions containers, so container-specific ATT&CK technique review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-25748 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 7.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L
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:L/A:L2.84.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.6HighVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://groups.google.com/g/kubernetes-security-announce/c/avaRYa9c7I8CVE reference
- https://github.com/kubernetes/ingress-nginx/issues/8686CVE reference
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.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.