CVE-2021-35515Network attack vector

Service hang via cyclic 7Z codec chain

Published Jul 13, 2021 · Updated Aug 4, 2024

Denial of service in Apache Commons Compress 1.6 through 1.20 allows remote attackers to hang services via a crafted 7Z archive. The sevenz Folder.getOrderedCoders method follows bind-pair indexes to build a decoder chain but, before reuse detection was added, a cyclic chain revisited the same Coder indefinitely. Exposure requires an application to pass attacker-controlled 7Z content to the sevenz parser; the resulting loop consumes processing time and stalls that service.

CVSS severity7.5
High
EPSS probability11.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Apache Commons Compress 1.6 through 1.20 allows remote attackers to hang services via a crafted 7Z archive. The sevenz Folder.getOrderedCoders method follows bind-pair indexes to build a decoder chain but, before reuse detection was added, a cyclic chain revisited the same Coder indefinitely. Exposure requires an application to pass attacker-controlled 7Z content to the sevenz parser; the resulting loop consumes processing time and stalls that service.

The record

CVE
CVE-2021-35515
Published
Jul 13, 2021
Updated
Aug 4, 2024
Vendor
The Apache Software Foundation
Product
Apache Commons Compress
Classifications
CWE-835, CWE-834, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 13, 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=1.6 <Apache Commons Compress*

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Commons Compressversion=1.6 <Apache Commons Compress*

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
7.5NIST NVDCVSS: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-835Loop with Unreachable Exit Condition ('Infinite Loop')
CWE-834Excessive Iteration
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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