CVE-2021-3331Network attack vector

Arbitrary program execution via unsafe session settings

Published Jan 27, 2021 · Updated Aug 3, 2024

Unsafe session-setting loading in WinSCP before 5.17.10 allows remote attackers to execute arbitrary programs through a crafted handled URL. ParseUrl applied URL-supplied raw settings to executable fields such as Shell, ListingCommand, PostLoginCommands, and proxy commands without marking the input unsafe. Exposure requires WinSCP to handle the crafted URL; a default installation registers it for sftp:// URLs, and successful exploitation runs attacker-chosen programs.

CVSS severity9.8
Critical
EPSS probability7.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unsafe session-setting loading in WinSCP before 5.17.10 allows remote attackers to execute arbitrary programs through a crafted handled URL. ParseUrl applied URL-supplied raw settings to executable fields such as Shell, ListingCommand, PostLoginCommands, and proxy commands without marking the input unsafe. Exposure requires WinSCP to handle the crafted URL; a default installation registers it for sftp:// URLs, and successful exploitation runs attacker-chosen programs.

The record

CVE
CVE-2021-3331
Published
Jan 27, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

10.0NIST NVDAV:N/AC:L/Au:N/C:C/I:C/A:C
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1204.001User Execution: Malicious Link

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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