CVE-2021-20285Public exploit

Process crash via unchecked ELF relocation offsets

Published Mar 26, 2021 · Updated Aug 3, 2024

Out-of-bounds memory access in The UPX Team's UPX 3.96 allows local users to crash the packer with a crafted ELF file. PackLinuxElf64::canPack in src/p_lx_elf.cpp trusts attacker-controlled DT_RELA and DT_RELASZ values, forms a relocation pointer outside file_image, and reads through it without validating either value against the input size. The file must be supplied to and processed by UPX; the demonstrated result is a segmentation fault that interrupts that UPX process, while other impacts remain unspecified.

CVSS severity6.6
Medium
EPSS probability0.75%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds memory access in The UPX Team's UPX 3.96 allows local users to crash the packer with a crafted ELF file. PackLinuxElf64::canPack in src/p_lx_elf.cpp trusts attacker-controlled DT_RELA and DT_RELASZ values, forms a relocation pointer outside file_image, and reads through it without validating either value against the input size. The file must be supplied to and processed by UPX; the demonstrated result is a segmentation fault that interrupts that UPX process, while other impacts remain unspecified.

The record

CVE
CVE-2021-20285
Published
Mar 26, 2021
Updated
Aug 3, 2024
Vendor
The UPX Team
Product
UPX
Classifications
CWE-787, CWE-119, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 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 3.96

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The UPX Team · UPXversion=UPX 3.96

Published CVSS scores

8.3NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:C
6.6NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/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-787Out-of-bounds Write
CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
T1203Exploitation for Client Execution

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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