CVE-2021-30477Network attack vector

Unauthorized private-stream messages via webhook replies

Published Apr 14, 2021 · Updated Aug 3, 2024

Improper access control in Zulip Server before 3.4 allows remote authenticated users to send messages to unauthorized private streams. The outgoing-webhook reply path accepts a bot-generated response without enforcing the initiating user's permission to post to the destination private stream. Access to an outgoing webhook bot is required; the bounded consequence is unauthorized message injection, not reading private content or interrupting service.

CVSS severity4.3
Medium
EPSS probability0.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Zulip Server before 3.4 allows remote authenticated users to send messages to unauthorized private streams. The outgoing-webhook reply path accepts a bot-generated response without enforcing the initiating user's permission to post to the destination private stream. Access to an outgoing webhook bot is required; the bounded consequence is unauthorized message injection, not reading private content or interrupting service.

The record

CVE
CVE-2021-30477
Published
Apr 14, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1565.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 14, 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 privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:P/A:N
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1565.001Stored Data Manipulation

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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