CVE-2021-30129Network attack vector

Unauthenticated server crash via unbounded pending writes

Published Jul 12, 2021 · Updated Aug 3, 2024

Resource exhaustion in Apache MINA SSHD 2.0.0 through 2.6.x allows remote attackers to crash SSH servers through stalled output. BufferedIoOutputStream queues writes without bounding pending bytes when an SFTP or forwarded-connection peer stops consuming data. No authentication or user interaction is required, and continued queued output consumes heap until the hosting Java process raises an OutOfMemoryError.

CVSS severity7.5
High
EPSS probability3.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Apache MINA SSHD 2.0.0 through 2.6.x allows remote attackers to crash SSH servers through stalled output. BufferedIoOutputStream queues writes without bounding pending bytes when an SFTP or forwarded-connection peer stops consuming data. No authentication or user interaction is required, and continued queued output consumes heap until the hosting Java process raises an OutOfMemoryError.

The record

CVE
CVE-2021-30129
Published
Jul 12, 2021
Updated
Aug 3, 2024
Vendor
The Apache Software Foundation
Product
Apache MINA SSHD
Classifications
CWE-772, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 12, 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?

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

  1. Affected versionversion=2.0.0 <Apache Mina SSHD* changes=[{"at":"2.7.0","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache MINA SSHDversion=2.0.0 <Apache Mina SSHD* changes=[{"at":"2.7.0","status":"unaffected"}]

Published CVSS scores

7.5GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-772Missing Release of Resource after Effective Lifetime
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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