CVE-2023-27538

Authentication bypass via overbroad SSH connection reuse

Published Mar 30, 2023 · Updated Jun 9, 2025

Authentication bypass in libcurl 7.16.1 through 7.88.1 allows attackers to reuse an SSH connection under unintended credentials. ConnectionExists in lib/url.c uses an equality test for the SSH protocol-family bitmask, preventing ssh_config_matches from rejecting a pooled connection after a key-file change. Reachability requires sequential SCP or SFTP transfers in one connection pool with a changed public- or private-key file, causing the later transfer to inherit the prior authenticated connection.

CVSS severity7.7
High
EPSS probability1.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Authentication bypass in libcurl 7.16.1 through 7.88.1 allows attackers to reuse an SSH connection under unintended credentials. ConnectionExists in lib/url.c uses an equality test for the SSH protocol-family bitmask, preventing ssh_config_matches from rejecting a pooled connection after a key-file change. Reachability requires sequential SCP or SFTP transfers in one connection pool with a changed public- or private-key file, causing the later transfer to inherit the prior authenticated connection.

The record

CVE
CVE-2023-27538
Published
Mar 30, 2023
Updated
Jun 9, 2025
Vendor
curl
Product
curl
Classifications
CWE-305, T1550
Attack vector
local
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

Compare your product and version with the public record. A matching version still requires validation against your environment.

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 vectorlocal
Required privilegesunauthenticated

What is affected?

curl · curlversion=Fixed in 8.0.0

Published CVSS scores

7.7CISA-ADPCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/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)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-305Authentication Bypass by Primary Weakness
T1550Use Alternate Authentication Material

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo