CVE-2021-28683
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 · uneditedAn issue was discovered in Envoy through 1.71.1. There is a remotely exploitable NULL pointer dereference and crash in TLS when an unknown TLS alert code is received.
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 through version 1.71.1 contains a remotely exploitable NULL pointer dereference vulnerability in its TLS implementation. When Envoy receives a TLS alert code that it does not recognize or handle, it attempts to dereference a NULL pointer, causing the process to crash and resulting in a denial of service.
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= 1.16.2= 1.17.1CVSS 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
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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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Identify Envoy versionRun 'envoy --version' or check the Docker image tag / binary name to determine the installed Envoy version.Affected if The installed version is between 1.16.2 and 1.71.1 inclusive (including 1.16.2 and 1.17.1 specifically).
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Verify TLS listener configurationReview Envoy configuration files (YAML/JSON) for any listener blocks with 'tls' transport_socket enabled, or run 'envoy --listeningPorts' to see active listeners.Affected if Envoy is configured with TLS listeners accepting connections from untrusted sources.
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Confirm network exposureCheck if TLS-enabled listeners are bound to interfaces accessible from untrusted networks (0.0.0.0 or public IPs) rather than only localhost or internal networks.Affected if Envoy TLS listeners are exposed to the internet or untrusted external clients who could send malicious TLS alerts.
A user is affected if their Envoy version falls within 1.16.2 through 1.71.1 and they operate TLS listeners exposed to untrusted network traffic that could trigger the NULL pointer dereference upon receipt of unrecognized TLS alert codes.
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 dataUpgrade Envoy to version 1.71.2 or later, which contains the fix for this TLS alert handling vulnerability. As an interim measure, consider implementing rate limiting or load balancer health checks to mitigate the impact of crash exploits.
- Consultation2.0 h
- Implementation8.0 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-2021-28683 — 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-2021-28683 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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