Apache Flink JobManager REST API Arbitrary File Read & Directory Traversal Vulnerability (CVE-2020-17519) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTApache Flink versions 1.11.0, 1.11.1, and 1.11.2
Unauthenticated remote attackers can read arbitrary files on the JobManager local filesystem via the REST interface
Immediately upgrade to Apache Flink 1.11.3, 1.12.0, or later versions
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
The recommended remediation is to upgrade Apache Flink to version 1.11.3 or 1.12.0 or higher.
# For Docker-based deployments, update your Dockerfile base image:
# Old: FROM flink:1.11.2
# New:
FROM flink:1.11.3-scala_2.12
# For Kubernetes Helm deployments, upgrade using the following command:
helm upgrade flink-release-name flink-charts/flink --set image.tag=1.11.32. Temporary Workaround & Hardening Configuration
If an immediate upgrade is not feasible, restrict access to the JobManager REST API port (8081) using firewalls, or deploy an Nginx reverse proxy to block malicious directory traversal patterns.
# Nginx configuration to block directory traversal attempts
server {
listen 80;
server_name flink.internal;
location / {
# Block requests containing directory traversal sequences
if ($request_uri ~* '(\.\./|\.\.%2f|%2e%2e%2f|%2e%2e%252f)') {
return 403 'Access Denied: Malicious Request Detected';
}
proxy_pass http://localhost:8081;
}
}3. Log Audit & IoC Verification Commands
Use the following Bash script to scan JobManager access logs for potential exploitation attempts.
#!/bin/bash
# Define Flink log directory
LOG_DIR='/opt/flink/log'
echo '[+] Scanning Flink logs for CVE-2020-17519 exploitation attempts...'
# Search for double-encoded dots and slashes in log files
grep -Ei '(%252f|%2e%2e|\.\./|jobmanager/logs)' $LOG_DIR/* 2>/dev/null
if [ $? -eq 0 ]; then
echo '[!] WARNING: Suspected directory traversal attempts detected!'
else
echo '[+] No suspicious patterns found.'
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2020-17519) is a directory traversal and arbitrary file read flaw introduced in Apache Flink 1.11.0. The root cause lies in the JobManager process's REST API endpoint, which fails to properly validate and sanitize user-supplied file path parameters. Consequently, attackers can leverage double URL-encoded directory traversal sequences (e.g., '%252f..%252f') to bypass access controls and read any file on the local filesystem that the JobManager process has permissions to access.
2. Exploitation Mechanics & Attack Scenario
An attacker can exploit this vulnerability by sending a crafted HTTP GET request to the JobManager's REST API port (default: 8081) without any authentication. By appending double URL-encoded traversal sequences to endpoints like '/jobmanager/logs/', the attacker can escape the intended log directory and retrieve sensitive system files such as '/etc/passwd' or Flink configuration files (flink-conf.yaml). This vulnerability is actively exploited in the wild and is listed in the CISA KEV catalog.
3. Infrastructure & Business Impact
Successful exploitation of this vulnerability can lead to the exposure of highly sensitive credentials, database connection strings, and cloud access keys stored in configuration files. This exposure facilitates lateral movement within the internal network, potentially leading to full cluster compromise, data exfiltration, and severe business disruption.
Official Vendor Advisories & References
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.
Frequently Asked SecOps Questions (CVE-2020-17519)
FAQQ1. How critical is CVE-2020-17519 and is it actively exploited in the wild?
CVE-2020-17519 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 98.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2020-17519?
Primary impacted vendors include apache across flink. Scope summary: Apache Flink versions 1.11.0, 1.11.1, and 1.11.2 with exposed JobManager REST API
Q3. What temporary mitigations or workarounds exist for CVE-2020-17519 before patching?
[Mitigation] Immediately upgrade to Apache Flink 1.11.3, 1.12.0, or later versions Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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