KEV Intelligence

Vulnerability report

Active exploitation observed Confirmed confidence Not in CISA KEV

CVE-2020-17518

Apache Flink Path Traversal

Apache Software Foundation / Apache Flink · Apache Flink 1.5.1 to 1.11.2

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Severity
CVSS 7.5 · High
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
50.0%
First observed
12 Jun 2026
Last observed
23 Jul 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2020-17518 is an unauthenticated vulnerability affecting Apache Software Foundation Apache Flink. Apache Flink 1.5.1 introduced a REST handler that allows you to write an uploaded file to an arbitrary location on...

Is it exploited?

Yes. KEV Intelligence sensors observed exploitation attempts with confirmed confidence.

Who is affected?

Apache Software Foundation / Apache Flink apache flink 1.5.1 to 1.11.2.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

Overview

Apache Flink Path Traversal

Apache Flink 1.5.1 introduced a REST handler that allows you to write an uploaded file to an arbitrary location on the local file system, through a maliciously modified HTTP HEADER. The files can be written to any location accessible by Flink 1.5.1.

All users should upgrade to Flink 1.11.3 or 1.12.0 if their Flink instance(s) are exposed. The issue was fixed in commit a5264a6f41524afe8ceadf1d8ddc8c80f323ebc4 from apache/flink:master.

Vendor Product Affected Status
Apache Software Foundation Apache Flink Apache Flink 1.5.1 to 1.11.2 Affected
Published
05 Jan 2021
Exploitation Reported
12 Jun 2026
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

nuclei_scanner apache

CVE References

Exploitation evidence

Why KEV Intelligence marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

KEV Intelligence

Recorded 12 Jun 2026

Independent exploitation attestation added to the KEV Intelligence record.

Active exploitation observed

KEV Intelligence sensor

First observed 12 Jun 2026

First-party sensor telemetry confirms matching exploitation attempts.

Proof of concept available

GitHub

Recorded 06 Jan 2021

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.

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Source Added
The Shadowserver First 2025-12-05 00:00 UTC
KEV Intelligence 2026-07-03 12:36 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Aggregate observations show the scale, recency, and distribution of activity without overstating sparse data.

2

Attempts observed

1

Unique attacker IPs

1

Attacker countries

US

1

Sensors observed

Exploitation attempts over the last 70 days

Daily events observed by KEV Intelligence sensors

Updated 19 Aug 2026

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68
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11 Jun 25 Jun 9 Jul 23 Jul 19 Aug

First observed 12 Jun 2026 · Last observed 23 Jul 2026

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Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
2
User-Agents
2

Raw values available in Pro and Enterprise.

Virtual patch status

No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

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Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

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Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2020/CVE-2020-17518.yaml 25 Apr 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

7.5 High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS

50.0%

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') CWE-22 Relative Path Traversal CWE-23

All CVSS Scores

CVSS v3.1 7.5 High

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

CVSS v2.0 5.0 Medium

AV:N/AC:L/Au:N/C:N/I:P/A:N

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

Apache Flink 1.5.1 - Local File Inclusion

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. Public PoC available

    Public proof-of-concept code published

  2. Observed by KEV Intelligence sensors

    Evidence-backed exploitation signal

  3. Indicators of compromise added (29)

    Indicators of compromise recorded

  4. Added to KEV Intelligence KEV Feed

    High-confidence, third-party attested exploitation

  5. Nuclei template available

    Scanner coverage available

  6. CVE published

    Vulnerability disclosed publicly

  7. CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2020-17518

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2020-17518",
  "confidence": "Confirmed",
  "cvss_score": 7.5,
  "cvss_estimated": false,
  "epss_score": 0.50038,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 2, "sensors": 1 }
}

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