CVE-2021-43312Public exploitNetwork attack vector

Process crash via unchecked GNU hash bucket count

Published Mar 24, 2023 · Updated Feb 25, 2025

Heap buffer overflow in UPX before 4.0.0-git-c6b9e3c62d15 allows attackers to crash the process by decompressing a crafted ELF file. PackLinuxElf64::invert_pt_dynamic uses the file-declared GNU hash bucket count to index bucket data without confirming that the allocation contains that many entries. Reaching the fault requires UPX to decompress the crafted file; the demonstrated consequence is an AddressSanitizer abort or segmentation fault.

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 buffer overflow in UPX before 4.0.0-git-c6b9e3c62d15 allows attackers to crash the process by decompressing a crafted ELF file. PackLinuxElf64::invert_pt_dynamic uses the file-declared GNU hash bucket count to index bucket data without confirming that the allocation contains that many entries. Reaching the fault requires UPX to decompress the crafted file; the demonstrated consequence is an AddressSanitizer abort or segmentation fault.

The record

CVE
CVE-2021-43312
Published
Mar 24, 2023
Updated
Feb 25, 2025
Vendor
The UPX Team
Product
UPX
Classifications
CWE-787, CWE-119
Attack vector
network
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 vectornetwork
Required privilegesunauthenticated

What is affected?

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

Published CVSS scores

7.5NIST National Vulnerability DatabaseCVSS: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.

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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)
Vectornetwork
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

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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