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CVE Record

CVE-2020-5403: DoS Via Malformed URL with Reactor Netty HTTP Server

Reactor 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.

MediumCVSS 6.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2020-5403 is an availability issue in Reactor Netty HTTP Server. A malformed URL can trigger an exception path where the server closes the connection prematurely instead of returning a normal 400 response. The reported impact is denial of service, not data theft or code execution.

Executive priority

Treat this as a moderate availability risk. It is most important for public or business-critical services using the affected Reactor Netty versions. Remediation should be scheduled promptly, but the sources do not support emergency active-exploitation handling.

Technical view

Reactor Netty HttpServer versions 0.9.3.RELEASE and 0.9.4.RELEASE mishandle malformed URL parsing, exposing a URISyntaxException behavior. The CVSS 3.0 score is 6.5, with network reachability, low attack complexity, no privileges required, and high availability impact.

Likely exposure

Exposure is likely limited to applications running Reactor Netty HttpServer 0.9.3.RELEASE or 0.9.4.RELEASE, especially if reachable over a network. The source bundle does not identify other affected products or downstream frameworks.

Exploitation context

The bundle does not indicate active exploitation, and KEV is false. The issue is described as network-reachable denial of service through malformed URL handling, but no public exploit status is provided in the supplied sources.

Researcher notes

Evidence is narrow: affected versions, behavior, CWE-20, CVSS, and vendor reference are provided. The bundle does not name a fixed version, workaround, exploit availability, or broader affected ecosystem, so validation should stay dependency-focused.

Mitigation direction

  • Inventory applications using Reactor Netty HttpServer.
  • Check for versions 0.9.3.RELEASE and 0.9.4.RELEASE.
  • Review the Pivotal advisory for the vendor-supported fix.
  • Upgrade according to vendor guidance after testing.
  • Prioritize externally reachable HTTP services first.
  • Monitor for abnormal connection closures and URL parsing errors.

Validation and detection

  • Review SBOMs, lockfiles, and dependency manifests for Reactor Netty versions.
  • Confirm runtime artifacts match the reviewed dependency versions.
  • Check whether affected services expose Reactor Netty HttpServer to network traffic.
  • Review logs for URISyntaxException-related connection closures.
  • Document affected and remediated services in vulnerability tracking.
Prepared
Confidence
high
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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

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cwe · low confidence lookup

CWE-20: Exact CWE lookup

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cve · low confidence lookup

CVE-2020-5403 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.5 (3.0)
Known Exploited
No
Published

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Official CVE source material

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.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We 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.

ScoreVersionSeverityVectorExploitImpactSource
6.5CVSS 3.0MediumCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H2.83.6Primary CVE score

Vulnerability scoring details

Base CVSS 3.0 score

6.5Medium
CVSS 3.0 vector shape for CVE-2020-5403Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
PivotalReactor Netty0.9 v0.9.3.RELEASE, 0.9 v0.9.4.RELEASEListed
Weakness

CWE details

CWE-20

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.