`CVE-2020-17518` Apache Flink

Affected software	Apache Flink
Severity	7.5 High CVSS 3.1 2 scores
Fixed in	`1.11.3`
Weakness	Relative path traversal (CWE-23)
Published	5 Jan 2021
Updated	17 Jun 2026

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.

CWE-22 · Path traversal

Exploitation status

Exploited

Real-world exploitation reported by VulnCheck KEV. CISA has not confirmed it.

CISA KEV not listed
VulnCheck KEV listed Exploitation reported in the wild. Honeypot sightings · 3 exploits · earliest 2023-11-25.
CISA Vulnrichment no assessment published
Indexed PoC 4 indexed Published artifacts you can open, in GitHub PoC, Nuclei; first seen 2021-01-06.
EPSS 49% chance in 30 days A model's forecast, not a report of exploitation. Higher than 99% of all scored CVEs.

VulnCheck KEV

Exploitation evidence from VulnCheck Known Exploited Vulnerabilities (VulnCheck KEV), used under VulnCheck's community terms. View CVE-2020-17518 in VulnCheck (free account).

Evidence	Source	Detail	Date
Honeypot sighting	Shadowserver honeypots	Exploitation attempts seen on 563 days	2023-11-25 to 2026-11-12
Exploit reference	VulnCheck XDB cbd3d87ea7d5	Exploit type: initial-access	2021-01-06
Exploit reference	VulnCheck XDB 03b52e0c11e3	Exploit type: initial-access	2021-01-10
Exploit reference	VulnCheck XDB d75c5445c328	Exploit type: initial-access	2021-01-10

Evidence

Source

Detail

Date

Honeypot sighting

Shadowserver honeypots

Exploitation attempts seen on 563 days

2023-11-25 to 2026-11-12

Exploit reference

VulnCheck XDB cbd3d87ea7d5

Exploit type: initial-access

2021-01-06

Exploit reference

VulnCheck XDB 03b52e0c11e3

Exploit type: initial-access

2021-01-10

Exploit reference

VulnCheck XDB d75c5445c328

Exploit type: initial-access

2021-01-10

2 of these are GitHub repositories with fewer than 5 stars. They are listed for reference and don't count toward the exploitation status above.

Index	Artifact	Stars	First seen
GitHub PoC	QmF0c3UK/CVE-2020-17518	7	2021-01-06
GitHub PoC	[CVE-2020-17518] Apache Flink RESTful API Arbitrary File Upload via Directory Traversal	3	2021-01-10
GitHub PoC	利用Apache Flink CVE-2020-17518 getshell	1	2021-01-10
Nuclei	Apache Flink 1.5.1 - Local File Inclusion

Waratek protection

Protected by Waratek

Waratek has a rule that blocks attacks on this vulnerability.

Protection full Path traversal
Action available security rule
Review automated Inferred
Record active

Decided by	A vulnerability class already blocked by an ARMR security rule
Finding	Protected by Waratek's ARMR path-traversal security rule, which blocks this class of attack at the JVM level without a rule written for this CVE specifically. The CVE's weakness is CWE-23: Relative Path Traversal.

Decided by

A vulnerability class already blocked by an ARMR security rule

Finding

Protected by Waratek's ARMR path-traversal security rule, which blocks this class of attack at the JVM level without a rule written for this CVE specifically. The CVE's weakness is CWE-23: Relative Path Traversal.

How to mitigate CVE-2020-17518

Upgrade Apache Flink to 1.11.3 or later. Until you can, Waratek RASP blocks exploitation with its path traversal rule. It runs inside the Java application, with no code changes.

Waratek RASP Runtime protection for Java applications

CVSS

7.5 HIGH v3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N 2 metrics

We show the highest score from the newest CVSS version. Scores from different versions can't be compared, and the first score listed is sometimes a 0.0 placeholder.

Version Score Band Vector Assigner Type

CVSS 3.1 7.5 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N NVD Primary published

CVSS 2.0 5.0 none AV:N/AC:L/Au:N/C:N/I:P/A:N NVD Primary

Version	Score	Band	Vector	Assigner	Type
CVSS 3.1	7.5	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`	NVD	Primary	published
CVSS 2.0	5.0	none	`AV:N/AC:L/Au:N/C:N/I:P/A:N`	NVD	Primary

Affected software and releases

Maven packages

Affected and fixed versions, from OSV.dev

Package Introduced Fixed Last affected

org.apache.flink:flink-runtime 1.5.1 1.11.3 unbounded

Package	Introduced	Fixed	Last affected
`org.apache.flink:flink-runtime`	1.5.1	`1.11.3`	unbounded

Products and versions

2 products, 2 version entries

Source	Vendor	Product	Scheme	Affected versions
nvd	apache	flink	generic	≥ 1.5.1 and ＜ 1.11.3
osv	org.apache.flink	flink-runtime	generic	≥ 1.5.1 and ＜ 1.11.3

Source

Vendor

Product

Scheme

Affected versions

nvd

apache

flink

generic

≥ 1.5.1 and ＜ 1.11.3

osv

org.apache.flink

flink-runtime

generic

≥ 1.5.1 and ＜ 1.11.3

References

URL	Tags
https://github.com/apache/flink/commit/a5264a6f41524afe8ceadf1d8ddc8c80f323ebc4	WEB
https://lists.apache.org/thread.html/rfe159ccf496d75813f24c6079c5d33872d83f5a2e39cb32c3aef5a73@%3Cissues.flink.apache.org%3E	WEB
https://lists.apache.org/thread.html/rf8812a5703f4a5f1341138baf239258b250875699732cfdf9d55b21d@%3Cissues.flink.apache.org%3E	WEB
https://lists.apache.org/thread.html/rec0d650fbd4ea1a5e1224a347d83a63cb44291c334ad58b8809bc23b@%3Cissues.flink.apache.org%3E	WEB
https://lists.apache.org/thread.html/rd6a1a0e2d73220a65a8f6535bbcd24bb66adb0d046c4a1aa18777cf3@%3Cdev.flink.apache.org%3E	WEB
https://lists.apache.org/thread.html/rd2467344f88bcaf108b8209ca92da8ec393c68174bfb8c27d1e20faa@%3Cdev.flink.apache.org%3E	WEB
https://lists.apache.org/thread.html/rcb9e8af775f2a3706b69153aefde78f208871649df057c70ce2e24f9@%3Cissues.flink.apache.org%3E	WEB
https://lists.apache.org/thread.html/rb43cd476419a48be89c1339b527a18116f23eec5b6df2b2acbfef261@%3Cuser.flink.apache.org%3E	WEB
https://lists.apache.org/thread.html/rb43cd476419a48be89c1339b527a18116f23eec5b6df2b2acbfef261@%3Cdev.flink.apache.org%3E	WEB
https://lists.apache.org/thread.html/rb43cd476419a48be89c1339b527a18116f23eec5b6df2b2acbfef261@%3Cannounce.apache.org%3E	WEB

URL

Timeline

Published	2021-01-05	By the CVE Program.
VulnCheck KEV: earliest evidence	2023-11-25	Date of the oldest evidence of exploitation in VulnCheck KEV's record. VulnCheck does not publish the date it listed the CVE.
NVD record modified	2026-06-17	NVD's own last-modified date for this record.
VulnCheck KEV: latest evidence	2026-11-12	Date of the newest report, exploit reference or honeypot sighting in VulnCheck KEV's record.

Published

2021-01-05

By the CVE Program.

VulnCheck KEV: earliest evidence

2023-11-25

Date of the oldest evidence of exploitation in VulnCheck KEV's record. VulnCheck does not publish the date it listed the CVE.

NVD record modified

2026-06-17

NVD's own last-modified date for this record.

VulnCheck KEV: latest evidence

2026-11-12

Date of the newest report, exploit reference or honeypot sighting in VulnCheck KEV's record.

How VRT decided (17 of 24 rules ran)

17 of 24 rules ran. The rest didn't run because an earlier rule had already settled the CVE.

# Rule Outcome Status Detail

identity: Does this identifier describe a vulnerability at all? the first rule that matches decides

1 rejected no match CVE Program withdrawal of this identifier

scope: Is it a vulnerability Waratek protects? the first rule that matches decides

2 armr-patch-file no match An ARMR patch file on disk for this CVE

3 armr-secure-rule-file no match An ARMR security-rule template on disk for this CVE

4 manual-classification no match A researcher's recorded decision for this specific CVE

5 manual classification no match Manual classification of this CVE in the legacy dataset

6 non-java-upstream no match A root cause in non-Java code: an OS kernel, a C library, or a bundled runtime

7 oracle-component no match The defect being in a component of a tracked product the agent does not reach: JavaFX, the Java SE installer, the JInitiator browser plug-in, the native WebLogic proxy plug-in, or a native part of Oracle Application Server or Collaboration Suite (HTTP Server, Web Cache, Internet Directory, mail and calendar servers). Oracle gives these no CPE of their own and names them only in the description.

8 java-client-side no match Oracle's own risk-matrix note saying the CVE is reached only through untrusted code in the Java sandbox (applets, Web Start) or only through a client installation of Java, so a server running its own trusted code is not exposed

9 osv-maven matched In scope Maven packages: org.apache.flink:flink-runtime

10 cna-maven-package not reached An affected Maven artifact named by the CNA itself

11 known-cpe-product not reached An NVD CPE naming a product ARMR tracks

12 cna-cpe-product not reached A CPE the CNA published naming a tracked product. Oracle publishes these on advisory day, months before NVD.

13 oracle-advisory-family not reached A tracked product family named in Oracle's own risk matrix. CPE cannot carry a suite name, only a module.

14 cna-named-product not reached A tracked product named in words by the CVE's own CNA, on a record with no CPE yet. Apache and Eclipse publish these on advisory day, before NVD adds CPE data.

15 non-deployable-product not reached The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached

16 unmatched-product not reached No tracked product matched above, and none present at all

disposition: What do we do about one that is? every rule runs

17 patch-hint no match A reference pointing at the upstream fix: a commit, a PR, a Red Hat bug

18 open-source-maven matched Mitigation candidate Open-source Maven artifact indexed by OSV (Maven packages: org.apache.flink:flink-runtime). The source is public, which makes an ARMR patch rule a candidate; nothing here establishes that one can be written.

19 poc-derivable skipped An indexed exploit clearing the evidence bar to reverse-engineer, where there is no source to read

20 no-exploit skipped Nothing to build a rule from yet: no published exploit, no CISA record of exploitation and no source-level change to read

21 secure-rule-match decided it matched Protected by Waratek CWE-23 (Relative Path Traversal) is mitigable by an ARMR path-traversal security rule.

22 exploited-no-fix-or-poc skipped Somebody exploiting this CVE (a CISA or VulnCheck KEV listing, or a CISA verdict of active exploitation), with no fix, source code or PoC to build a rule from

23 below-action-threshold skipped Medium or Low severity, no CISA or VulnCheck KEV listing, no PoC clearing the evidence bar, no CISA verdict, no Oracle advisory

24 no-exploit-published skipped Exploit code for this candidate, published in a reviewed catalogue or a GitHub repository with 5 or more stars, or in use per CISA or VulnCheck; not only a CISA verdict, a forecast, or nothing at all

Products the scope rules checked

The products this CVE's record names, and whether VRT tracks each one. The scope rules decided on these.

Vendor Product Tracked CPE Source

apache flink not tracked cpe:2.3:a:apache:flink:*:*:*:*:*:*:*:*

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