CVE-2021-41163Network attack vector

Unauthenticated RCE via pipe-prefixed subscription URL

Published Oct 20, 2021 · Updated Aug 4, 2024

OS command injection in Discourse before 2.7.9 stable or 2.8.0.beta7 beta allows remote attackers to execute code via SNS webhooks. The ConfirmSnsSubscription job passes a verified message's subscribe_url to Kernel.open, which treats a pipe-prefixed value as a command; the patch parses it as a URI and uses Net::HTTP instead. No Discourse account or user interaction is required, and self-hosted instances expose the webhook route even when AWS SNS is unused.

CVSS severity9.8
Critical
EPSS probability19.81%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OS command injection in Discourse before 2.7.9 stable or 2.8.0.beta7 beta allows remote attackers to execute code via SNS webhooks. The ConfirmSnsSubscription job passes a verified message's subscribe_url to Kernel.open, which treats a pipe-prefixed value as a command; the patch parses it as a URI and uses Net::HTTP instead. No Discourse account or user interaction is required, and self-hosted instances expose the webhook route even when AWS SNS is unused.

The record

CVE
CVE-2021-41163
Published
Oct 20, 2021
Updated
Aug 4, 2024
Vendor
Discourse
Product
Discourse
Classifications
CWE-74, CWE-78, T1059
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 20, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=beta < 2.8.0.beta7
  2. Affected versionversion=stable < 2.7.9
  3. Affected versionversion=tests-passed < 2.8.0.beta7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Discourse · Discourseversion=beta < 2.8.0.beta7; version=stable < 2.7.9; version=tests-passed < 2.8.0.beta7

Published CVSS scores

9.8NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
10.0GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
7.5NVDAV:N/AC:L/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-74Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
CWE-78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
T1059Command and Scripting Interpreter

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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