CVE-2021-28831Network attack vector

Decompression crash via error-tagged result pointer

Published Mar 19, 2021 · Updated Dec 17, 2025

Improper error handling in BusyBox 1.32.1 and earlier allows remote attackers to crash gzip decompression with malformed data. In decompress_gunzip.c, huft_build can encode an error in the low bit of its result pointer, but the cleanup path treats the tagged value as a valid allocation and attempts to free it. Exploitation requires BusyBox to process attacker-supplied gzip content; the bounded consequence is an invalid free or segmentation fault in the decompression process.

CVSS severity7.5
High
EPSS probability2.72%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper error handling in BusyBox 1.32.1 and earlier allows remote attackers to crash gzip decompression with malformed data. In decompress_gunzip.c, huft_build can encode an error in the low bit of its result pointer, but the cleanup path treats the tagged value as a valid allocation and attempts to free it. Exploitation requires BusyBox to process attacker-supplied gzip content; the bounded consequence is an invalid free or segmentation fault in the decompression process.

The record

CVE
CVE-2021-28831
Published
Mar 19, 2021
Updated
Dec 17, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-755, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Dec 17, 2025Record 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

7.5MITRECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/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 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-755Improper Handling of Exceptional Conditions
T1499.004Application or System Exploitation

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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