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CVE Record

CVE-2021-4249: xml-conduit DOCTYPE Entity Expansion Parse.hs infinite loop

A vulnerability was found in xml-conduit. It has been classified as problematic. Affected is an unknown function of the file xml-conduit/src/Text/XML/Stream/Parse.hs of the component DOCTYPE Entity Expansion Handler. The manipulation leads to infinite loop. It is possible to launch the attack remotely. Upgrading to version 1.9.1.0 is able to address this issue. The name of the patch is 4be1021791dcdee8b164d239433a2043dc0939ea. It is recommended to upgrade the affected component. The identifier of this vulnerability is VDB-216204.

MediumCVSS 4.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-4249 affects Haskell's xml-conduit library. Specially crafted XML involving DOCTYPE entity expansion can cause an infinite loop, reducing availability. It is not a data theft or privilege escalation issue in the provided sources, but services that parse untrusted XML may hang or degrade until the dependency is upgraded.

Executive priority

Handle in normal patch cadence, faster for internet-facing or partner-facing XML processing. Business risk is service degradation rather than direct compromise based on provided evidence. Lack of active-exploitation evidence lowers urgency, but simple dependency remediation is available.

Technical view

The issue is in xml-conduit/src/Text/XML/Stream/Parse.hs, within DOCTYPE entity expansion handling. Affected versions run through 1.9.0.0, and version 1.9.1.0 includes the referenced fix commit 4be1021791dcdee8b164d239433a2043dc0939ea. CVSS 3.1 is 4.3: network reachable, low complexity, no privileges, user interaction required, low availability impact.

Likely exposure

Exposure is most likely in Haskell applications or services that depend on xml-conduit versions 0.5.0 through 1.9.0.0 and parse XML influenced by users, partners, uploads, feeds, or integrations. The source bundle provides no CPEs, so dependency inventory is the most reliable exposure check.

Exploitation context

The sources state remote attack is possible and CVSS indicates user interaction is required. No KEV listing is present, and the provided bundle does not cite active exploitation, public exploit use, or observed attacks. Treat exploit status as unconfirmed rather than active.

Researcher notes

The record identifies CWE-404 and an infinite-loop condition in DOCTYPE entity expansion handling. Affected function details are not fully named in the bundle. Validation should focus on dependency versioning and XML input paths; avoid assuming broader XML parser impacts beyond xml-conduit.

Mitigation direction

  • Upgrade xml-conduit to version 1.9.1.0 or later.
  • Prioritize systems that parse externally supplied XML.
  • Review the upstream PR and commit for parser behavior changes.
  • If upgrade timing is uncertain, check current upstream package guidance.

Validation and detection

  • Inventory Haskell dependencies for xml-conduit versions through 1.9.0.0.
  • Confirm deployed builds use xml-conduit 1.9.1.0 or later.
  • Identify routes, jobs, or integrations that parse untrusted XML.
  • Check monitoring for XML parsing hangs or availability degradation.
Prepared
Confidence
medium
Sources
6

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

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ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-404: Exact CWE lookup

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cve · low confidence lookup

CVE-2021-4249 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
4.3 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

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
5Source 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
4.3CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L2.81.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

4.3Medium
CVSS 3.1 vector shape for CVE-2021-4249Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L

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
unspecifiedxml-conduit0.5.0, 0.5.0.1, 0.5.1, 0.5.1.1, 0.5.1.2, 0.5.2, 0.5.3, 0.5.3.1, 0.5.4, 0.6.0, 0.6.1, 0.7.0, 0.7.0.1, 0.7.0.2, 0.7.0.3, 1.0.0, 1.0.1, 1.0.1.1, 1.0.2, 1.0.2.1, 1.0.3, 1.0.3.1, 1.0.3.2, 1.0.3.3, 1.1.0, 1.1.0.1, 1.1.0.2, 1.1.0.3, 1.1.0.4, 1.1.0.5, 1.1.0.6, 1.1.0.7, 1.1.0.8, 1.1.0.9, 1.2.0, 1.2.0.1, 1.2.0.2, 1.2.0.3, 1.2.1, 1.2.1.1, 1.2.2, 1.2.3, 1.2.3.1, 1.2.3.2, 1.2.3.3, 1.2.4, 1.2.5, 1.2.5.1, 1.2.6, 1.3.0, 1.3.1, 1.3.2, 1.3.3, 1.3.3.1, 1.3.4, 1.3.4.1, 1.3.4.2, 1.3.5, 1.4.0, 1.4.0.1, 1.4.0.2, 1.4.0.3, 1.4.0.4, 1.5.0, 1.5.1, 1.6.0, 1.7.0, 1.7.0.1, 1.7.1.0, 1.7.1.1, 1.7.1.2, 1.8.0, 1.8.0.1, 1.9.0.0Listed
Weakness

CWE details

CWE-404

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

CWE-404 · source CWE mapping

Improper Resource Shutdown or Release

Improper Resource Shutdown or Release represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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