CVE-2021-43317Public exploit

Denial of service via unchecked ELF hash chains

Published Mar 24, 2023 · Updated Feb 25, 2025

Heap-based buffer overflow in UPX before 4.0.0-git-c6b9e3c62d15 allows local users to crash the utility by unpacking a crafted ELF64 file. PackLinuxElf64::elf_lookup uses values from crafted ELF hash buckets as indexes into the chain table without bounds checks, so get_le32 reads beyond the allocated heap buffer. The crafted file must enter the decompression path; the published proof of concept produces a process abort and service interruption, with no reported code execution.

CVSS severity7.5
High
EPSS probability0.82%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in UPX before 4.0.0-git-c6b9e3c62d15 allows local users to crash the utility by unpacking a crafted ELF64 file. PackLinuxElf64::elf_lookup uses values from crafted ELF hash buckets as indexes into the chain table without bounds checks, so get_le32 reads beyond the allocated heap buffer. The crafted file must enter the decompression path; the published proof of concept produces a process abort and service interruption, with no reported code execution.

The record

CVE
CVE-2021-43317
Published
Mar 24, 2023
Updated
Feb 25, 2025
Vendor
The UPX Team
Product
UPX
Classifications
CWE-787, CWE-119, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 24, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 25, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=upx before 4.0.0-git-c6b9e3c62d15

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The UPX Team · UPXversion=upx before 4.0.0-git-c6b9e3c62d15

Published CVSS scores

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.

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)
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
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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