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Actively exploited

CVE-2020-17519 Apache Flink Improper Access Control Vulnerability

Apache Flink contains an improper access control vulnerability that allows an attacker to read any file on the local filesystem of the JobManager through its REST interface.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 23 May 2024.
  • Rated Critical severity (CVSS 9.1, scored by CISA).
  • It has been in the catalogue for 897 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

A change introduced in Apache Flink 1.11.0 (and released in 1.11.1 and 1.11.2 as well) allows attackers to read any file on the local filesystem of the JobManager through the REST interface of the JobManager process. Access is restricted to files accessible by the JobManager process. 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 b561010b0ee741543c3953306037f00d7a9f0801 from apache/flink:master.

Affected Versions

ProductVersions
Apache Software Foundation Apache FlinkApache Flink 1.11.0 to 1.11.2

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Apache Flink. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 13 Jun 2024 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2020-17519
  3. CVE record: CVE-2020-17519
  4. FIRST EPSS
  5. lists.apache.org/thread.html/r6843202556a6d0bce9607ebc02e303f68fc88e9038235598bde3b50d%40%3Cdev.flin
  6. lists.apache.org/thread.html/r6843202556a6d0bce9607ebc02e303f68fc88e9038235598bde3b50d%40%3Cuser.fli
  7. lists.apache.org/thread.html/r6843202556a6d0bce9607ebc02e303f68fc88e9038235598bde3b50d%40%3Cannounce
  8. openwall.com/lists/oss-security/2021/01/05/2
  9. lists.apache.org/thread.html/r28f17e564950d663e68cc6fe75756012dda62ac623766bb9bc5e7034%40%3Cissues.f
  10. packetstormsecurity.com/files/160849/Apache-Flink-1.11.0-Arbitrary-File-Read-Directory-Traversal.htm
  11. lists.apache.org/thread.html/r2fc60b30557e4a537c2a6293023049bd1c49fd92b518309aa85a0398%40%3Cissues.f