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CVE Record

CVE-2021-23427: Arbitrary File Write via Archive Extraction (Zip Slip)

This affects all versions of package elFinder.NetCore. The ExtractAsync function within the FileSystem is vulnerable to arbitrary extraction due to insufficient validation.

HighCVSS 8.6Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

elFinder.NetCore’s archive extraction can write files outside the intended extraction area because paths are not sufficiently validated. In a vulnerable application, a crafted archive could cause sensitive files to be overwritten or new files to be placed where the application account can write.

Executive priority

Treat as high priority for internet-facing or user-upload workflows. The issue can cross from a file-management feature into broader application compromise depending on write permissions and file placement. Prioritize inventory and containment first, then vendor-confirmed remediation.

Technical view

CVE-2021-23427 affects elFinder.NetCore. The source bundle identifies FileSystem.ExtractAsync as vulnerable to arbitrary extraction, commonly described as Zip Slip. The CVSS 3.1 score is 8.6 high, with network attack vector, no privileges, no user interaction, high confidentiality impact, and low integrity and availability impact.

Likely exposure

Applications using elFinder.NetCore and exposing archive extraction through FileSystem.ExtractAsync are the likely exposure point. Risk is higher where untrusted users can upload or trigger extraction of archives. The bundle states all versions are affected but does not enumerate downstream applications.

Exploitation context

The provided sources do not show CISA KEV listing or cited active exploitation. Exploitation requires the vulnerable extraction behavior to be reachable in an application. The public bundle confirms the vulnerable function and arbitrary file write condition but does not provide evidence of real-world attacks.

Researcher notes

Evidence is strongest for the vulnerable component and function, not for exploitation in the wild. The source bundle does not identify a patch version, CWE mapping, or KEV status beyond false. Avoid assuming impact beyond filesystem write capability available to the application process.

Mitigation direction

  • Check elFinder.NetCore vendor or package guidance for fixed versions or official remediation.
  • Disable or restrict archive extraction for untrusted users until remediation is confirmed.
  • Run affected applications with least-privilege filesystem permissions.
  • Review upload and extraction paths for unexpected file creation or overwrites.
  • Add monitoring for writes outside intended storage directories.

Validation and detection

  • Inventory applications and dependencies for elFinder.NetCore usage.
  • Confirm whether FileSystem.ExtractAsync or archive extraction is exposed to users.
  • Review configuration and application routes that accept archive uploads.
  • Check filesystem permissions for the application runtime account.
  • Look for unexpected files written near web roots or configuration directories.
Prepared
Confidence
medium
Sources
4

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.

description · low confidence lookup

File access behavior lookup

The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-23427 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
8.6 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L/E:F/RL:U/RC:C

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
3Source 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
8.6CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L/E:F/RL:U/RC:C3.94.7Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

8.6High
CVSS 3.1 vector shape for CVE-2021-23427Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L/E:F/RL:U/RC:C

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
n/aelFinder.NetCore0Listed
Weakness

CWE details

No CWE listed

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