CVE-2020-17518: 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…

PriorityP183high7.5CVSS 3.1

AVNACLPRNUINSUCNIHAN

ITWEXPLOITVulnCheck KEVInitial access

Exploited in the wild

EPSS

50.04%

98.8th percentile

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

3 ranges

Vendor	Product	Version range	Fixed in
apache	flink	—	—
apache	flink	>= 1.5.1 < 1.11.3	1.11.3
apache_software_foundation	apache_flink	—	—

Detection & IOCsextracted from sources · hover to see the quote

urlPOST /jars/upload HTTP/1.1

path/jars/upload

path/jobmanager/logs/..%252f..%252f..%252f..%252f..%252f..%252f..%252f..%252f..%252f..%252f..%252f..%252ftmp%252fpoc

filename../../../../../../../tmp/poc

hasha5264a6f41524afe8ceadf1d8ddc8c80f323ebc4↗

→Detect path traversal upload attempts targeting the Apache Flink REST API: look for POST requests to /jars/upload containing a multipart Content-Disposition filename field with directory traversal sequences (e.g., '../' or URL-encoded variants).
→Detect path traversal read attempts via the Flink log endpoint: look for GET requests to /jobmanager/logs/ containing double-URL-encoded traversal sequences (%252f).
→The exploit uses a two-stage attack: (1) upload a file with a traversal path in the filename header to write to an arbitrary location, then (2) retrieve it via the log endpoint using double-percent-encoded traversal. Correlate POST /jars/upload followed by GET /jobmanager/logs/..%25 from the same source IP. ↗
→Nuclei template matcher: a successful exploit is confirmed when the response body of the second request (GET to traversal path) contains the random string uploaded in the POST body and returns HTTP 200.

·Affected versions are Apache Flink 1.5.1 through 1.11.2; the vulnerability was introduced in 1.5.1. Only instances with the REST API exposed are exploitable. ↗
·Files can only be written to locations accessible by the Flink process user; privilege escalation beyond the Flink service account is not directly implied. ↗

CVSS provenance

nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

nvdv2.05.0MEDIUMAV:N/AC:L/Au:N/C:N/I:P/A:N

vulncheck7.5HIGH

vendor_apache7.5HIGH

vendor_redhat7.5HIGH

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