CVE-2020-6835Network attack vector

Service crash via mishandled file-read error

Published Jan 10, 2020 · Updated Aug 4, 2024

Heap corruption in Bftpd before 5.4 allows remote attackers to trigger a one-byte overwrite when a file-transfer read fails. The command_retr loop treats read() returning -1 as true, then writes a NUL byte to buffer[-1] instead of stopping on the error. The trigger requires a failed read during file download; the demonstrated consequence is a server crash or one-byte heap corruption.

CVSS severity9.8
Critical
EPSS probability2.02%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap corruption in Bftpd before 5.4 allows remote attackers to trigger a one-byte overwrite when a file-transfer read fails. The command_retr loop treats read() returning -1 as true, then writes a NUL byte to buffer[-1] instead of stopping on the error. The trigger requires a failed read during file download; the demonstrated consequence is a server crash or one-byte heap corruption.

The record

CVE
CVE-2020-6835
Published
Jan 10, 2020
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-193, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 10, 2020CVE 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-193Off-by-one Error
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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