CVE-2020-17518 | Apache Flink directory traversal attack: remote file writing through the REST API

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.

Published: 2021-01-05 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]

Conclusion & alert: CVE-2020-17518 is rated Moderate Risk (64.8/100): CVSS High severity, with high exploitation likelihood (EPSS 93.80%, 100th percentile). Core evidence: EPSS ranks this CVE among the most likely to be exploited in the near term. Mandatory action: High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2020-17518

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-03 93.95% 93.80% -0.14%
2 2026-05-13 93.98% 93.95% -0.03%
3 2026-05-07 93.98%

Full EPSS history (35 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-17518

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
10.0 2.9 [email protected]

Weakness enumeration for CVE-2020-17518

GitHub Security Advisory for CVE-2020-17518

GHSA-7q5g-gph2-4rc6 · Severity: high · Ecosystem: maven — Upload of file to arbitrary path in Apache Flink

OS Trackers for CVE-2020-17518

vendor priority summary link
redhat medium https://access.redhat.com/security/cve/CVE-2020-17518

Affected software / configurations for CVE-2020-17518

Vendor Product Version Raw CPE
apache flink >= 1.5.1, < 1.11.3 cpe:2.3:a:apache:flink:*:*:*:*:*:*:*:*

References for CVE-2020-17518

URL Tags
http://www.openwall.com/lists/oss-security/2021/01/05/1 Mailing List Third Party Advisory
https://lists.apache.org/thread.html/r0b000dc028616d33cb9aa388eb45d516b789cab0024dad94bc06588a%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r1125f3044a0946d1e7e6f125a6170b58d413ebd4a95157e4608041c7%40%3Cannounce.apache.org%3E
https://lists.apache.org/thread.html/r229167538863518738e02f4c1c5a8bb34c1d45dadcc97adf6676b0c1%40%3Cdev.flink.apache.org%3E
https://lists.apache.org/thread.html/r26fcdd4fe288323006253437ebc4dd6fdfadfb5e93465a0e4f68420d%40%3Cuser-zh.flink.apache.org%3E
https://lists.apache.org/thread.html/r28f17e564950d663e68cc6fe75756012dda62ac623766bb9bc5e7034%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r4a87837518804b31eb9db3048347ed2bb7b46fbaad5844f22a9fd4dc%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r5444acac3407ef6397d6aef1b5aec2db53b4b88ef221e63084c1e5f2%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r705fb2211b82c9f1f8d2b1d4c823bcbca50402ba09b96608ec657efe%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r710693b0d3b229c81f485804ea1145b4edda79c9e77d66c39a0a2ff1%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r7b2ee88c66fc1d0823e66475631f5c3e7f0365204ff0cb094d9f2433%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r8167f30c4c60a11b8d5be3f55537beeda629be61196e693bde403b36%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r88200d2f0b620c6b4b1585a7171355005c89e678b01d0e71a16c57e7%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/r90890afea72a9571d666820b2fe5942a0a5f86be406fa31da3dd0922%40%3Cannounce.apache.org%3E
https://lists.apache.org/thread.html/ra8c96bf3ccb4e491f9ce87ba35f134b4449beb2a38d1ce28fd89001f%40%3Cdev.flink.apache.org%3E
https://lists.apache.org/thread.html/rb43cd476419a48be89c1339b527a18116f23eec5b6df2b2acbfef261%40%3Cannounce.apache.org%3E
https://lists.apache.org/thread.html/rb43cd476419a48be89c1339b527a18116f23eec5b6df2b2acbfef261%40%3Cdev.flink.apache.org%3E Mailing List Vendor Advisory
https://lists.apache.org/thread.html/rb43cd476419a48be89c1339b527a18116f23eec5b6df2b2acbfef261%40%3Cuser.flink.apache.org%3E
https://lists.apache.org/thread.html/rcb9e8af775f2a3706b69153aefde78f208871649df057c70ce2e24f9%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/rd2467344f88bcaf108b8209ca92da8ec393c68174bfb8c27d1e20faa%40%3Cdev.flink.apache.org%3E
https://lists.apache.org/thread.html/rd6a1a0e2d73220a65a8f6535bbcd24bb66adb0d046c4a1aa18777cf3%40%3Cdev.flink.apache.org%3E
https://lists.apache.org/thread.html/rec0d650fbd4ea1a5e1224a347d83a63cb44291c334ad58b8809bc23b%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/rf8812a5703f4a5f1341138baf239258b250875699732cfdf9d55b21d%40%3Cissues.flink.apache.org%3E
https://lists.apache.org/thread.html/rfe159ccf496d75813f24c6079c5d33872d83f5a2e39cb32c3aef5a73%40%3Cissues.flink.apache.org%3E
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