CVE-2021-43311Public exploitNetwork attack vector

Service crash via unchecked ELF symbol lookup

Published Mar 24, 2023 · Updated Feb 25, 2025

Heap-based buffer overflow in The UPX Team UPX before 4.0.0-git-c6b9e3c62d15 allows attackers to crash UPX via a crafted ELF file. PackLinuxElf32::elf_lookup passes unchecked hash-table-derived pointers to get_le32, which performs a four-byte read beyond the allocated heap buffer. Exploitation requires UPX to process attacker-controlled ELF input; the demonstrated consequence is an abort or segmentation fault, not 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 The UPX Team UPX before 4.0.0-git-c6b9e3c62d15 allows attackers to crash UPX via a crafted ELF file. PackLinuxElf32::elf_lookup passes unchecked hash-table-derived pointers to get_le32, which performs a four-byte read beyond the allocated heap buffer. Exploitation requires UPX to process attacker-controlled ELF input; the demonstrated consequence is an abort or segmentation fault, not code execution.

The record

CVE
CVE-2021-43311
Published
Mar 24, 2023
Updated
Feb 25, 2025
Vendor
The UPX Team
Product
UPX
Classifications
CWE-787, CWE-119, T1499.004
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 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)
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
T1499.004Application 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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