CVE-2020-27801Public exploit

Unpacker crash via unchecked Mach-O bounds

Published Aug 25, 2022 · Updated Aug 4, 2024

A heap-based buffer over-read in The UPX Team UPX 4.0.0 allows attackers to interrupt unpacking via a crafted Mach-O file. During unpacking, get_le64 in bele.h reads eight bytes without confirming that the heap buffer contains that many bytes, allowing a malformed Mach-O structure to reach memory beyond the allocation. The attacker must cause a local user or automated workflow to process the crafted file; the demonstrated consequence is a process crash and possible memory disclosure, with no evidence of remote reachability.

CVSS severity7.8
High
EPSS probability0.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A heap-based buffer over-read in The UPX Team UPX 4.0.0 allows attackers to interrupt unpacking via a crafted Mach-O file. During unpacking, get_le64 in bele.h reads eight bytes without confirming that the heap buffer contains that many bytes, allowing a malformed Mach-O structure to reach memory beyond the allocation. The attacker must cause a local user or automated workflow to process the crafted file; the demonstrated consequence is a process crash and possible memory disclosure, with no evidence of remote reachability.

The record

CVE
CVE-2020-27801
Published
Aug 25, 2022
Updated
Aug 4, 2024
Vendor
The UPX Team
Product
UPX
Classifications
CWE-119, CWE-125, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 25, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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 4.0.0-git-87b73e5cfdc1+

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

The UPX Team · UPXversion=upx 4.0.0-git-87b73e5cfdc1+

Published CVSS scores

7.8NVDCVSS: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-119Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-125Out-of-bounds Read
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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