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CVE-2020-17519

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Apache Flink. For every flaw being used in attacks, see Exploited flaws; for Apache’s, see Apache flaws being used in attacks.

CVE-2020-17519 is a security flaw in Apache Flink, open-source software from the Apache Software Foundation. Attackers can reach parts of Apache Flink that should be locked to them. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 23 May 2024.[1]

Apache Flink is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Apache has published a fix or advice.

Description

CISA calls it an improper access control in Apache Flink. In its words: “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.”[1]

The CVE record adds: “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.”[2]

The underlying weakness is CWE-552, in MITRE’s list of common software weaknesses.

It scores 7.5 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record doesn’t list version ranges for it; Apache’s advisory has them[3]. CISA names the product as Apache Flink.

Most families won’t have Apache Flink; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 23 May 2024, 1,234 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 13 Jun 2024 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 98%. That’s in the top 1% of the flaws it scores.[4]

CISA assesses it as automatable: attackers can run it against many targets at once.

CISA doesn’t say who was attacked, or how.

Fix

Apache has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.”[1]

  1. Check whether you use it.Apache Flink is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 13 Jun 2024 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 7.5.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 98%.[4]

See also

Other Apache flaws

  • CVE-2016-3081, Apache Struts: command injection ·
  • CVE-2026-34486, Apache Tomcat: missing encryption of sensitive data ·
  • CVE-2026-34197, Apache ActiveMQ: improper input validation ·
  • CVE-2024-38475, Apache HTTP Server: improper escaping of output ·
  • CVE-2025-24813, Apache Tomcat: path equivalence ·

Similar flaws

  • CVE-2026-21589, Atlassian products: files or directories accessible to external parties ·
  • CVE-2025-11371, Gladinet CentreStack and Triofox: files or directories accessible to external parties ·
  • CVE-2017-16651, Roundcube Webmail: webmail file disclosure ·

Every Apache flaw on CISA’s list · Everything added in May 2024

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Apache Flink Improper Access Control Vulnerability”. Known Exploited Vulnerabilities Catalog, added 23 May 2024.
  2. ^ National Institute of Standards and Technology. “CVE-2020-17519 Detail”. National Vulnerability Database, published 5 Jan 2021.
  3. ^ Apache. Advisories and fixes: lists.apache.org, lists.apache.org, lists.apache.org, lists.apache.org, lists.apache.org, and 1 more on NVD’s record.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.980, percentile 99.9, 31 Oct 2026.
  5. CVE Program. “CVE-2020-17519”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.