Security readout for executives and security teams
Plain-English summary
Envoy could make access-control decisions on a URL path before decoding escaped slash or backslash characters. If a backend decoded those characters differently, a blocked sensitive path could still be reached. This matters most where Envoy enforces RBAC or JWT rules based on URL paths.
Executive priority
Treat as high priority for Envoy deployments protecting administrative or sensitive routes by path. Prioritize internet-facing gateways and service meshes where Envoy makes authorization decisions before forwarding to application backends.
Technical view
CVE-2021-29492 affects Envoy versions 1.18.2 and earlier. Envoy did not decode escaped slash sequences in HTTP URL paths before path-based RBAC or JWT enforcement. Backends that normalize those characters as path separators could interpret the request as targeting a different protected resource, causing privilege escalation.
Likely exposure
Exposure is likely when Envoy <= 1.18.2 fronts untrusted HTTP clients, uses RBAC or JWT filters with URL-path matching, and sends traffic to backends that treat escaped and literal slash or backslash characters interchangeably.
Exploitation context
The source bundle does not report known active exploitation, and KEV status is false. Exploitation requires a specific mismatch between Envoy path matching and backend path decoding, which aligns with the CVSS high severity but higher attack complexity.
Researcher notes
The core condition is parser inconsistency: Envoy path matching versus backend path decoding and normalization. Evidence supports privilege escalation risk, but not active exploitation. Validation should focus on affected Envoy versions, path-based RBAC/JWT enforcement, and backend treatment of encoded separators.
Mitigation direction
- Upgrade Envoy to a patched branch release: 1.18.3, 1.17.3, 1.16.4, or 1.15.5.
- Configure the patched path normalization option to decode escaped slash characters where applicable.
- If patching is delayed, reconfigure backends not to treat escaped and literal separators interchangeably.
- Review RBAC and JWT policies that authorize requests based on URL path.
- Check vendor guidance for branch-specific configuration details before deployment.
Validation and detection
- Inventory Envoy versions and confirm no affected versions remain in service.
- Identify RBAC or JWT filters that enforce authorization using URL-path matches.
- Confirm backend frameworks do not normalize escaped separators differently from Envoy.
- Review access logs for untrusted requests containing escaped slash or backslash characters.
- Regression-test protected routes through Envoy and backend path handling 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
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ATT&CK lookup starting points
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CWE-22: File access and web shell behavior lookup
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Open ATT&CK lookupCVE-2021-29492 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 8.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/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:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.1HighVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-4987-27fx-x6cfCVE 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.
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.