CVE-2021-30501Public exploit

Process abort via zero-length Mach-O allocation

Published May 26, 2021 · Updated Aug 3, 2024

Reachable assertion in MemBuffer::alloc in The UPX Team UPX 4.0.0 allows local users to abort UPX via a crafted Mach-O file. PackMachBase::canUnpack passes an unvalidated zero Mach_header.sizeofcmds value to rawmseg_buf.alloc, whose size-greater-than-zero assertion terminates the process. A user must make UPX decompress the crafted file, and the demonstrated consequence is limited to termination of that invoked UPX process.

CVSS severity5.5
Medium
EPSS probability1.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reachable assertion in MemBuffer::alloc in The UPX Team UPX 4.0.0 allows local users to abort UPX via a crafted Mach-O file. PackMachBase::canUnpack passes an unvalidated zero Mach_header.sizeofcmds value to rawmseg_buf.alloc, whose size-greater-than-zero assertion terminates the process. A user must make UPX decompress the crafted file, and the demonstrated consequence is limited to termination of that invoked UPX process.

The record

CVE
CVE-2021-30501
Published
May 26, 2021
Updated
Aug 3, 2024
Vendor
The UPX Team
Product
UPX
Classifications
CWE-617, CWE-20, T1499.004
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 26, 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=upx 4.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The UPX Team · UPXversion=upx 4.0

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-617Reachable Assertion
CWE-20Improper Input Validation
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

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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