How severe is CVE-2020-17518?

CVE-2020-17518 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2020-17518?

CVE-2020-17518 affects the following packages: org.apache.flink:flink-runtime (Maven). Ecosystems affected: Maven.

How do I fix CVE-2020-17518?

Update org.apache.flink:flink-runtime to version 1.11.3 or later. Run your dependency manager's update command and verify no transitive dependencies pin the vulnerable version. Use O3 Security's SCA scanner to confirm the fix is applied across your entire dependency tree.

Is CVE-2020-17518 actively exploited in the wild?

Yes. There are 5 known exploit references for CVE-2020-17518, including 3 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2020-17518?

CVE-2020-17518 has an EPSS (Exploit Prediction Scoring System) score of 93.8%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2020-17518?

CVE-2020-17518 is classified as CWE-23 (CWE-23), Path Traversal (CWE-22). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Is there exploit tooling available for CVE-2020-17518?

A Nuclei detection template exists for CVE-2020-17518, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2020-17518 published, and has it been updated?

CVE-2020-17518 was published on January 5, 2021 and was last updated on April 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕ Maven

CVE-2020-17518

HIGH

Upload of file to arbitrary path in Apache Flink

Also known asBIT-flink-2020-17518GHSA-7q5g-gph2-4rc6

Published

Jan 5, 2021

Updated

Apr 10, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

5 known

EPSS Exploitation Probability

via FIRST.org ↗

93.8%probability of exploitation in next 30 days

Very High Risk100th percentile-0.14%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

☕org.apache.flink:flink-runtime

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.flink:flink-runtime`	≥ 1.5.1&&< 1.11.3	1.11.3

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Apache Flink 1.5.1 introduced a REST handler that allows you to write an…

lists.apache.orgNVDMar 2021

Apache Flink 1.5.1 introduced a REST handler that allows you to write an…

github.comGithubJan 2021

Apache Flink 1.5.1 introduced a REST handler that allows you to write an…

github.comGithubJan 2021

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2020-17518 in your stack?

O3 detects CVE-2020-17518 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my stack How O3 SCA works