⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Critical · CVSS 9.1 ⚠ ACTIVELY EXPLOITED — CISA KEV

How to Fix CVE-2020-17519: Files Accessible to External Parties in Apache Flink

By Sai Kiran Pandrala

⚡ At a glance
SeverityCVSS 9.1 - Critical
Actively exploited?Yes, listed in CISA KEV (added 2024-05-23)
AffectedApache Flink Apache Flink 1.11.0 to 1.11.2
Fixed inSee vendor advisory
Type (CWE)CWE-552: Files or Directories Accessible to External Parties

Patch immediately. CISA added CVE-2020-17519 to the Known Exploited Vulnerabilities catalog on 2024-05-23. Federal civilian agencies must remediate by 2024-06-13. Treat every internet-reachable instance as a priority patch.

What is CVE-2020-17519?

CVE-2020-17519 is a Files Accessible to External Parties flaw in Apache Software Foundation Apache Flink. It carries a CVSS base score of 9.1 (critical). CISA confirmed real-world exploitation by adding it to the Known Exploited Vulnerabilities catalog on 2024-05-23.

From the source record: 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.

Why it matters in practice: KEV-listed CVEs draw continuous internet-wide scanning. Any unpatched, internet-reachable installation is on borrowed time. The blast radius depends on how the affected service is exposed. An internet-facing instance with no compensating controls is the highest-risk configuration.

Am I affected?

You are affected if your installation of Apache Flink matches a version listed in the Affected row above.

Check the installed binary:


apachectl -v          # Apache HTTPD
nginx -v              # Nginx
cat $CATALINA_HOME/RELEASE-NOTES | head -5  # Tomcat

How to fix CVE-2020-17519

Apply the vendor patch. Target the patched build listed on the vendor advisory. The runnable command set below covers the most common deployment patterns for Apache Flink.

Linux package upgrade


# Debian / Ubuntu
sudo apt-get update
sudo apt-get install --only-upgrade apache
# RHEL / Rocky
sudo dnf upgrade apache --security -y
# Then restart
sudo systemctl restart apache
apache -v

After applying the patch

  1. Restart the service or device so the patched binary loads.
  2. Confirm the running version matches the Fixed in row using the verification command below.
  3. Rotate credentials and API keys that the affected service could access if the asset was exposed during the disclosure window.

If you can't patch immediately

Until the patch lands, narrow the attack surface with these runnable controls.

Block exposure with nftables


sudo nft add table inet filter 2>/dev/null
sudo nft add chain inet filter input "{ type filter hook input priority 0 ; }" 2>/dev/null
sudo nft add rule inet filter input ip saddr 10.10.10.0/24 tcp dport 443 accept
sudo nft add rule inet filter input tcp dport 443 drop

WAF / reverse-proxy snippet

Block requests that look like the exploit pattern at the edge. Tune the regex to the published indicators in the vendor advisory:


# nginx
location / {
    if ($request_uri ~* "(\.\./|%2e%2e|<script|union\s+select)") { return 403; }
    proxy_pass http://backend;
}

Mitigations are temporary. Apply the vendor patch as soon as a maintenance window opens.

How to verify the fix worked

Confirm the patched build is the one actually running.


apache -v
# or for Apache HTTPD
apachectl -v

Expected: See vendor advisory or newer.

Also worth doing: pull recent log windows for any indicators of compromise listed in the vendor advisory, and re-run an authenticated vulnerability scan with up-to-date signatures.

Frequently asked questions

Other vulnerabilities in the same area that are worth patching alongside this one:

Is CVE-2020-17519 being exploited in the wild?

Yes. CISA added CVE-2020-17519 to the Known Exploited Vulnerabilities catalog on 2024-05-23. KEV listing means at least one confirmed real-world exploitation report exists.

Do I have to take downtime to patch?

For most Apache Software Foundation Apache Flink deployments, the patched build needs a service restart or device reboot. HA pairs and clusters can roll the upgrade by patching the standby first, failing over, then patching the former primary.

Will a WAF or IDS rule alone close CVE-2020-17519?

No. Network filters cut down opportunistic scans but they do not remove the flaw. The vendor patch is the only durable fix.

Why is CVE-2020-17519 rated critical?

The CVSS base score of 9.1 reflects network reach, low attack complexity, and high impact on confidentiality, integrity, and availability. That combination is what the rating model maps to critical.

References

*Assembled from the official vendor advisory, the NVD record, and the CISA KEV listing on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*