CVE-2021-30500Public exploit

Process crash via unchecked ELF header

Published May 26, 2021 · Updated Aug 3, 2024

Null pointer dereference in UPX 4.0 allows context-dependent attackers to crash the command-line process via a crafted file. PackLinuxElf::canUnpack processes input as ELF without first validating its header, leading get_le32 to read through a null pointer. A user must invoke UPX decompression on attacker-supplied input; the upstream evidence demonstrates a process abort but not code execution.

CVSS severity7.8
High
EPSS probability1.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Null pointer dereference in UPX 4.0 allows context-dependent attackers to crash the command-line process via a crafted file. PackLinuxElf::canUnpack processes input as ELF without first validating its header, leading get_le32 to read through a null pointer. A user must invoke UPX decompression on attacker-supplied input; the upstream evidence demonstrates a process abort but not code execution.

The record

CVE
CVE-2021-30500
Published
May 26, 2021
Updated
Aug 3, 2024
Vendor
The UPX Team
Product
UPX
Classifications
CWE-476, T1204.002
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

6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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-476NULL Pointer Dereference
T1204.002User Execution: Malicious File

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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