CVE-2021-29492
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedEnvoy is a cloud-native edge/middle/service proxy. Envoy does not decode escaped slash sequences `%2F` and `%5C` in HTTP URL paths in versions 1.18.2 and before. A remote attacker may craft a path with escaped slashes, e.g. `/something%2F..%2Fadmin`, to bypass access control, e.g. a block on `/admin`. A backend server could then decode slash sequences and normalize path and provide an attacker access beyond the scope provided for by the access control policy. ### Impact Escalation of Privileges when using RBAC or JWT filters with enforcement based on URL path. Users with back end servers that interpret `%2F` and `/` and `%5C` and `\` interchangeably are impacted. ### Attack Vector URL paths containing escaped slash characters delivered by untrusted client. Patches in versions 1.18.3, 1.17.3, 1.16.4, 1.15.5 contain new path normalization option to decode escaped slash characters. As a workaround, if back end servers treat `%2F` and `/` and `%5C` and `\` interchangeably and a URL path based access control is configured, one may reconfigure the back end server to not treat `%2F` and `/` and `%5C` and `\` interchangeably.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceEnvoy proxy versions 1.18.2 and before fail to decode escaped slash sequences (%2F for / and %5C for \) in HTTP URL paths before applying access control policies, allowing attackers to bypass RBAC or JWT path-based restrictions using crafted URLs like /something%2F..%2Fadmin.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 1.15.5>= 1.16.0, < 1.16.4>= 1.17.0, < 1.17.3>= 1.18.0, < 1.18.3CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Determine Envoy proxy versionRun 'envoy --version' or check the Docker image tag, or look for the version in the Envoy binary metadataAffected if The version is < 1.15.5, >= 1.16.0 and < 1.16.4, >= 1.17.0 and < 1.17.3, or >= 1.18.0 and < 1.18.3
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Identify if RBAC filter is configuredInspect your Envoy configuration (static or dynamic) for 'envoy.filters.http.rbac' in the HTTP filter chainAffected if RBAC filter is present and uses path-based rules to grant or deny access
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Identify if JWT authentication is configuredInspect your Envoy configuration for 'envoy.filters.http.jwt_authn' and check if any rule specifies path requirementsAffected if JWT verification is enabled with path-based authorization rules
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Check for path normalization configurationLook for 'normalize_path: true' or 'merge_slashes: true' in the route configuration or listener settingsAffected if Path normalization is not enabled or explicitly disabled (vulnerable configurations do not decode %2F before policy evaluation)
You are affected if you run a vulnerable Envoy version AND have RBAC or JWT path-based access policies configured without proper path normalization enabled.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data1.15.51.16.41.17.3
Upgrade to Envoy versions 1.18.3, 1.17.3, 1.16.4, or 1.15.5 which contain the new path normalization option to decode escaped slash characters, or ensure backend servers do not treat %2F and / interchangeably.
- Consultation3.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-29492 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-29492 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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