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 1.11.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-17518 is resolved across your whole dependency graph.

How do I detect CVE-2020-17518 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.flink:flink-runtime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2020-17518 if there is no patch (or I can't update yet)?

Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

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 49.1%, placing it in the 99th 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. This score warrants monitoring and prompt remediation.

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 October 24, 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

Not in CISA KEV

HIGH severity

CVE-2020-17518 — flink-runtime

HIGHFix: apache/flink@a5264a6

CVE-2020-17518 is a high-severity (CVSS 7.5) CWE-23 vulnerability in org.apache.flink:flink-runtime. 5 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for org.apache.flink:flink-runtime — see the affected versions and patch details below.

Upload of file to arbitrary path in Apache Flink

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

Published

Jan 5, 2021

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

5 known

Exploitation data as of Oct 30, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

49.1%probability of exploitation in next 30 days

High Risk-2.29%

Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

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`org.apache.flink:flink-runtime:1.11.3`

Affected Products

1 product · 1 configurations

Application

flinkapache

≥ 1.5.1 && < 1.11.3

range

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

Report on github.com

github.comGithubJan 2021

Report on github.com

github.comGithubJan 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.flink:flink-runtime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.flink:flink-runtime to 1.11.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-17518 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

How to detect CVE-2020-17518

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2020-17518 -u https://target

Template: Apache Flink 1.5.1 - Local File Inclusion
Severity: high
Impact: An attacker can exploit this vulnerability to access sensitive information, such as configuration files, credentials, or other sensitive data stored on the server.
Remediation: Upgrade Apache Flink to a version that is not affected by the vulnerability (1.5.2 or later).

Template by ProjectDiscovery nuclei-templates (pdteam), MIT licensed. View the full template. Scan only systems you are authorised to test.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Product	Fixed in	Advisory
Red Hat Fuse 7.9	`flink`	RHSA-2021:3140
Red Hat Integration	see advisory	RHSA-2021:3205
Red Hat Integration Camel Quarkus 2	see advisory	RHSA-2021:3207

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2020-17518 in your dependencies?

Find it across Maven, including transitive dependencies.

Scan my dependencies How O3 SCA works