CVE-2020-5403
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 · uneditedReactor Netty HttpServer, versions 0.9.3 and 0.9.4, is exposed to a URISyntaxException that causes the connection to be closed prematurely instead of producing a 400 response.
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 · moderate confidenceReactor Netty HttpServer versions 0.9.3 and 0.9.4 improperly handle malformed URIs containing syntax errors, throwing a URISyntaxException that terminates the connection instead of returning a 400 Bad Request response. This creates a denial-of-service vector where attackers can close connections by sending specially crafted malformed URI requests.
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= 0.9.3= 0.9.4CVSS 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 Reactor Netty dependencySearch project dependencies (Maven pom.xml, Gradle build.gradle, or JAR manifest) for 'reactor-netty' or 'reactor-extra' libraries. Check runtime classpath for reactor-netty*.jar files.Affected if Reactor Netty library is present in the application dependencies or classpath.
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Determine Reactor Netty versionLocate the specific version of reactor-netty artifact in your dependency management (pom.xml, build.gradle, MANIFEST.MF in JAR, or mvn/gradle dependency tree output). Compare against affected versions 0.9.3 and 0.9.4.Affected if The installed version is exactly 0.9.3 or exactly 0.9.4.
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Verify HttpServer usageSearch codebase for imports of 'reactor.netty.http.server.HttpServer' or usage of 'HttpServer.create()' method. Check if application configures an HTTP server using Reactor Netty.Affected if The application creates and starts an HttpServer instance using Reactor Netty.
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Check network exposureInspect server startup configuration or container deployment descriptors to determine if the HttpServer binds to a reachable network interface (0.0.0.0 or specific IP) and port.Affected if The HttpServer is exposed on a network-accessible interface, allowing external clients to send requests.
You are affected only if your application uses Reactor Netty HttpServer version exactly 0.9.3 or exactly 0.9.4, creates an HTTP server with it, and that server is network-accessible to attackers.
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 Reactor Netty to a version beyond 0.9.4 where the URISyntaxException is properly caught and returns a 400 response instead of closing the connection.
- Consultation2.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-5403 — 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-2020-5403 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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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- 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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