CVE-2021-37840Public exploitNetwork attack vector

Remote command execution via missing WebSocket origin validation

Published Aug 2, 2021 · Updated Aug 4, 2024

Cross-site WebSocket hijacking in aaPanel through 6.8.12 allows remote attackers to execute OS commands on managed servers via /webssh. The /webssh endpoint initializes SSH WebSocket sessions without validating the Origin header, so a malicious site can send command messages through the victim's authenticated browser. Exploitation requires a logged-in user with at least one Terminal host to visit an attacker-controlled site in a susceptible browser, and successful commands run on the configured managed instance.

CVSS severity8.8
High
EPSS probability1.68%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site WebSocket hijacking in aaPanel through 6.8.12 allows remote attackers to execute OS commands on managed servers via /webssh. The /webssh endpoint initializes SSH WebSocket sessions without validating the Origin header, so a malicious site can send command messages through the victim's authenticated browser. Exploitation requires a logged-in user with at least one Terminal host to visit an attacker-controlled site in a susceptible browser, and successful commands run on the configured managed instance.

The record

CVE
CVE-2021-37840
Published
Aug 2, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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

8.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
6.8NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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 exploitPublished

Weakness, pattern, technique

T1203Exploitation for Client Execution

Public exploit references

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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