CVE-2023-27535Public exploitNetwork attack vector

Unauthorized data access via mismatched FTP connection reuse

Published Mar 30, 2023 · Updated Jun 9, 2025

Authentication bypass in curl 7.13.0 through 7.88.1 allows remote attackers to access sensitive data via reused FTP connections. The ConnectionExists logic in lib/url.c omitted FTP account, alternate-user, SSL-use, and clear-command-channel settings when matching pooled connections. Exploitation requires sequential FTP transfers to the same endpoint with changed settings, causing a later transfer to run under the earlier connection's credential context.

CVSS severity5.9
Medium
EPSS probability1.61%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in curl 7.13.0 through 7.88.1 allows remote attackers to access sensitive data via reused FTP connections. The ConnectionExists logic in lib/url.c omitted FTP account, alternate-user, SSL-use, and clear-command-channel settings when matching pooled connections. Exploitation requires sequential FTP transfers to the same endpoint with changed settings, causing a later transfer to run under the earlier connection's credential context.

The record

CVE
CVE-2023-27535
Published
Mar 30, 2023
Updated
Jun 9, 2025
Vendor
curl
Product
curl
Classifications
CWE-305
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 30, 2023CVE publishedPublication date reported by the CVE source.
  2. Jun 9, 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=Fixed in 8.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=Fixed in 8.0.0

Published CVSS scores

5.9CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

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-305Authentication Bypass by Primary Weakness

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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