CVE-2020-1747

A vulnerability was discovered in the PyYAML library in versions before 5.3.1, where it is susceptible to arbitrary code execution when it processes untrusted YAML files through the full_load method or with the FullLoader loader. Applications that use the library to process untrusted input may be vulnerable to this flaw. An attacker could use this flaw to execute arbitrary code on the system by abusing the python/object/new constructor.

Published: 2020-03-24 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2020-1747 is rated High Risk (74.7/100): CVSS Critical severity, with high exploitation likelihood (EPSS 5.30%, 92th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +3.45% over the last day, indicating growing attacker interest. 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-2020-1747

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 2026-06-15 1.85% 5.30% +3.45%
2 2026-04-25 3.07% 1.85% -1.22%
3 2025-12-18 — 3.07% —

Full EPSS history (24 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2020-1747

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H 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:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H 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:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
10.0 2.0 HIGH
AV:N/AC:L/Au:N/C:C/I:C/A:C 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:C)
Complete confidentiality impact.
Integrity impact (I:C)
Complete integrity impact.
Availability impact (A:C)
Complete availability impact.
 10.0 10.0 [email protected]

Weakness enumeration for CVE-2020-1747

GitHub Security Advisory for CVE-2020-1747

GHSA-6757-jp84-gxfx · Severity: critical · Ecosystem: pip — Improper Input Validation in PyYAML

OS Trackers for CVE-2020-1747

vendor priority summary link
alpine critical CVE-2020-1747: 1 source package rows (py3-yaml); 9 state rows across 9 repos (3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 9, open 0. https://security.alpinelinux.org/vuln/CVE-2020-1747
debian not yet assigned CVE-2020-1747 not yet assigned priority: Debian including 1 source packages (pyyaml), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2020-1747
redhat medium — https://access.redhat.com/security/cve/CVE-2020-1747
suse high CVE-2020-1747 severity important: SUSE including 109 source package names (0.1.75:python3-PyYAML-5.1.2-6.6.1, 1.1.1.0.1.5.295:python3-PyYAML-5.1.2-6.6.1, …), 222 product×package rows across 82 product lines (Container caasp/v4/k8s-sidecar, Container ses/6/cephcsi/cephcsi, … (82 product lines)): Fixed 175, Known Not Affected 47. https://www.suse.com/security/cve/CVE-2020-1747/
ubuntu low CVE-2020-1747 low priority: Ubuntu including 1 source packages (pyyaml), 6 status rows across 6 suites (bionic, eoan, focal, trusty, upstream, xenial): not-affected 4, ignored 1, needs-triage 1. https://ubuntu.com/security/CVE-2020-1747

Affected software / configurations for CVE-2020-1747

Vendor Product Version Raw CPE
pyyaml pyyaml >= 5.1, < 5.3.1 cpe:2.3:a:pyyaml:pyyaml:*:*:*:*:*:*:*:*
fedoraproject fedora 30 cpe:2.3:o:fedoraproject:fedora:30:*:*:*:*:*:*:*
fedoraproject fedora 31 cpe:2.3:o:fedoraproject:fedora:31:*:*:*:*:*:*:*
fedoraproject fedora 32 cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
opensuse leap 15.1 cpe:2.3:o:opensuse:leap:15.1:*:*:*:*:*:*:*
oracle communications_cloud_native_core_network_function_cloud_native_environment 22.1.0 cpe:2.3:a:oracle:communications_cloud_native_core_network_function_cloud_native_environment:22.1.0:*:*:*:*:*:*:*

References for CVE-2020-1747

URL Tags
http://lists.opensuse.org/opensuse-security-announce/2020-04/msg00017.html Mailing List Third Party Advisory
http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00017.html Mailing List Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2020-1747 Issue Tracking Patch Third Party Advisory
https://github.com/yaml/pyyaml/pull/386 Patch Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/7PPAS6C4SZRDQLR7C22A5U3QOLXY33JX/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/K5HEPD7LEVDPCITY5IMDYWXUMX37VFMY/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/MMQXSZXNJT6ERABJZAAICI3DQSQLCP3D/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WORRFHPQVAFKKXXWLSSW6XKUYLWM6CSH/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ZBJA3SGNJKCAYPSHOHWY3KBCWNM5NYK2/
https://www.oracle.com/security-alerts/cpujul2022.html Patch Third Party Advisory
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