Security readout for executives and security teams
Plain-English summary
This CVE affects Istio deployments where a gateway uses AUTO_PASSTHROUGH routing. In that configuration, an outside client may reach services that should not be exposed and bypass intended authorization checks. The source bundle does not provide a CVSS score, but the described impact is serious for service-mesh environments.
Executive priority
Prioritize this for internet-facing or partner-facing Istio gateways. The business risk is unauthorized access to internal services through a trusted ingress path, but urgency depends on whether affected versions and AUTO_PASSTHROUGH are present.
Technical view
Istio before 1.8.6 and 1.9.x before 1.9.5 is affected. The vulnerable condition is tied to AUTO_PASSTHROUGH gateway routing, allowing remote access to unexpected in-cluster services while bypassing authorization checks. No CWE, CVSS vector, or broader product matrix is provided in the bundle.
Likely exposure
Exposure is limited to Istio clusters running affected versions with gateways configured for AUTO_PASSTHROUGH. Environments without Istio, without affected versions, or without that gateway mode are not shown as affected by the provided sources.
Exploitation context
The sources describe the issue as remotely exploitable, but the bundle does not cite active exploitation, public exploitation, or CISA KEV inclusion. Treat exposure as configuration-dependent until validated against the cluster.
Researcher notes
The evidence is narrow but clear: affected Istio versions plus AUTO_PASSTHROUGH gateway routing. The bundle lacks CVSS, CWE, exploit telemetry, and workaround detail beyond fixed-version boundaries. Validation should focus on mesh versioning, gateway mode, and unintended service reachability.
Mitigation direction
- Upgrade Istio 1.8 deployments to 1.8.6 or later.
- Upgrade Istio 1.9 deployments to 1.9.5 or later.
- Review Istio’s advisory for any current vendor guidance.
- Identify gateways using AUTO_PASSTHROUGH and reduce unnecessary external exposure.
- Recheck authorization assumptions for services reachable through affected gateways.
Validation and detection
- Inventory Istio versions across all clusters and namespaces.
- List gateway configurations and identify AUTO_PASSTHROUGH usage.
- Confirm exposed gateways do not route to unintended internal services.
- Review gateway access logs for unexpected external service access.
- Document unaffected clusters with version and gateway configuration evidence.
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.
CVE-2021-31921 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
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
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 and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://istio.io/latest/news/security/istio-security-2021-006/CVE reference · x_refsource_MISC
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.