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CVE Record

CVE-2026-26278: fast-xml-parser affected by DoS through entity expansion in DOCTYPE (no expansion limit)

fast-xml-parser allows users to validate XML, parse XML to JS object, or build XML from JS object without C/C++ based libraries and no callback. In versions 4.1.3 through 5.3.5, the XML parser can be forced to do an unlimited amount of entity expansion. With a very small XML input, it’s possible to make the parser spend seconds or even minutes processing a single request, effectively freezing the application. Version 5.3.6 fixes the issue. As a workaround, avoid using DOCTYPE parsing by `processEntities: false` option.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This flaw lets a tiny XML document make applications using fast-xml-parser spend excessive CPU time expanding entities. The business impact is availability: exposed services that parse untrusted XML could freeze or become slow enough to deny service.

Executive priority

Treat as a high-priority availability issue for internet-facing or partner-facing XML processing. Patch promptly, especially where service uptime or request isolation is business-critical.

Technical view

CVE-2026-26278 is CWE-776 entity expansion without a limit in fast-xml-parser. Listed affected ranges are 4.1.3 to before 4.5.4 and 5.0.0 to before 5.3.6. CVSS is 7.5: network-reachable, low complexity, unauthenticated, no user interaction, availability impact only.

Likely exposure

Exposure is most likely in Node.js applications or bundled products that accept XML from users, partners, APIs, uploads, queues, or webhooks and parse it with affected fast-xml-parser versions.

Exploitation context

The source bundle does not show CISA KEV listing or cited evidence of active exploitation. The advisory describes denial of service from very small XML input, but this analysis does not include exploit steps.

Researcher notes

The evidence supports a resource-exhaustion issue in DOCTYPE entity expansion. The bundle names fixed 5.3.6 and workaround processEntities:false. It does not provide KEV status, exploit telemetry, or enough detail to claim confidentiality or integrity impact.

Mitigation direction

  • Upgrade fast-xml-parser to version 5.3.6 or another vendor-confirmed unaffected version.
  • For 4.x deployments, confirm remediation against vendor guidance and affected-version ranges.
  • Where upgrade is pending, avoid DOCTYPE parsing with processEntities set to false.
  • Reduce exposure of endpoints that parse untrusted XML until remediation is complete.
  • Apply relevant Red Hat advisories where affected packaged products are in use.

Validation and detection

  • Inventory direct and transitive fast-xml-parser dependencies in applications and container images.
  • Confirm deployed versions are outside the affected ranges listed in the advisory.
  • Map every service path that accepts XML from untrusted or semi-trusted sources.
  • Verify parser configuration disables entity processing where used as a workaround.
  • Review runtime monitoring for CPU saturation or request stalls on XML-handling routes.
Prepared
Confidence
high
Sources
12

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-776: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-26278 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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.

2CVSS vectors
5Timeline events
2ADP providers
11Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6GitHub_M
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-26278Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPfast-xml-parser: fast-xml-parser: Denial of Service via unlimited XML entity expansion
other:Red Hat severity ratingcvssV3_1
  • 2026-02-19T21:03:33.363Z: Reported to Red Hat.
  • 2026-02-19T19:40:55.842Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
NaturalIntelligencefast-xml-parser>= 5.0.0, < 5.3.6, >= 4.1.3, < 4.5.4Listed
Weakness

CWE details

CWE-776

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

CWE-776 · source CWE mapping

Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')

Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs