CVE-2023-27535: An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse feature that can r

Q: How urgent is CVE-2023-27535?

Priority 55/100. Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

This week

MEDIUM 5.9REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2023-27535 is a medium-severity flaw (CVSS 5.9) affecting libcurl, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse feature that can result in wrong credentials being used during subsequent transfers. Previously created connections are kept in a connection pool for reuse if they match the current setup. However, certain FTP settings such as CURLOPT_FTP_ACCOUNT, CURLOPT_FTP_ALTERNATIVE_TO_USER, CURLOPT_FTP_SSL_CCC, and CURLOPT_USE_SSL were not included in the configurati

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.9 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	1.8% (top 22%)
CISA exploited list	No
Weakness	CWE-305, CWE-287
Published	2023-03-30
Last modified	2026-10-24

Publisher (CNA): HackerOne · Vendor: debian · fedoraproject · haxx · netapp

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2023-03-30 20:15 UTCPublished CVE record published
2026-10-24 13:10 UTCUpdated Record last modified

haxx libcurl UPGRADE

Affected: >= 7.13.0 and <= 7.88.1

Fixed in: newer than 7.88.1

Safe to downgrade to: a release before 7.13.0

1. Check installed version

apt-cache policy libcurl || rpm -q libcurl || libcurl --version

2. UPGRADE to newer than 7.88.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade libcurl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libcurl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 7.13.0 (Debian / Ubuntu)

apt-cache madison libcurl sudo apt install libcurl=<VERSION_BEFORE_7.13.0> sudo apt-mark hold libcurl

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list libcurl sudo dnf downgrade libcurl-<VERSION_BEFORE_7.13.0> sudo dnf versionlock add libcurl

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

fedoraproject fedora MITIGATE

Affected: 36

Fixed in: no fixed release known

Safe to downgrade to: a release before 36

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

debian debian linux MITIGATE

Affected: 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 10.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

netapp active iq unified manager MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy active-iq-unified-manager || rpm -q active-iq-unified-manager || active-iq-unified-manager --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

netapp ontap 9 MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy ontap-9 || rpm -q ontap-9 || ontap-9 --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

netapp h300s firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · gnome-shell-extension-tiling-assistant · FIXED · 56-1.fc46 · FEDORA-2026-ebf66a5321 · source

sudo dnf upgrade --advisory=FEDORA-2026-ebf66a5321

Ubuntu 20.04 · curl · FIXED · 7.68.0-1ubuntu2.18

sudo apt update && sudo apt install --only-upgrade curl dpkg --compare-versions "$(dpkg-query -W -f='${Version}' curl)" ge "7.68.0-1ubuntu2.18" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 22.04 · curl · FIXED · 7.81.0-1ubuntu1.10

sudo apt update && sudo apt install --only-upgrade curl dpkg --compare-versions "$(dpkg-query -W -f='${Version}' curl)" ge "7.81.0-1ubuntu1.10" && echo PATCHED || echo STILL-VULNERABLE

Debian 12 · curl · FIXED · 7.88.1-7

sudo apt update && sudo apt install --only-upgrade curl dpkg --compare-versions "$(dpkg-query -W -f='${Version}' curl)" ge "7.88.1-7" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · curl · FIXED · 7.88.1-7

sudo apt update && sudo apt install --only-upgrade curl dpkg --compare-versions "$(dpkg-query -W -f='${Version}' curl)" ge "7.88.1-7" && echo PATCHED || echo STILL-VULNERABLE

RHEL 8 · curl · FIXED · curl-7.61.1-30.el8_8.2

sudo dnf upgrade --advisory=RHSA-2023:3106 rpm -q curl

RHEL 8.6 Extended Update Support · curl · FIXED · curl-7.61.1-22.el8_6.12

sudo dnf upgrade --advisory=RHSA-2024:0428 rpm -q curl

RHEL 9 · curl · FIXED · curl-7.76.1-23.el9_2.1

sudo dnf upgrade --advisory=RHSA-2023:2650 rpm -q curl

RHEL 6 · curl · DEFERRED

RHEL 7 · curl · DEFERRED

Alpine 3.20 · curl · FIXED · curl-8.0.0-r0

apk add --upgrade curl apk info -v curl

Alpine 3.21 · curl · FIXED · curl-8.0.0-r0

apk add --upgrade curl apk info -v curl

Alpine 3.22 · curl · FIXED · curl-8.0.0-r0

apk add --upgrade curl apk info -v curl

Alpine 3.23 · curl · FIXED · curl-8.0.0-r0

apk add --upgrade curl apk info -v curl

Amazon Linux 2023 · see advisory · FIXED · ALAS2023-2023-193 · source

sudo dnf update --advisory=ALAS2023-2023-193

Amazon Linux 2 · see advisory · FIXED · ALAS2-2023-2070 · source

sudo yum update --advisory=ALAS2-2023-2070

Amazon Linux 1 · see advisory · FIXED · ALAS-2023-1727 · source

sudo yum update --advisory=ALAS-2023-1727

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2023-27535?

libcurl: upgrade to newer than 7.88.1; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2023-27535 being exploited?

CVE-2023-27535 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2023-27535 affect?

CVE-2023-27535 affects libcurl, fedora, debian linux. Severity is medium (CVSS 5.9). An authentication bypass vulnerability exists in libcurl <8.0.0 in the FTP connection reuse feature that can result in wrong credentials being used during subsequent transfers. Previously created connections are kept in a connection pool fo

How urgent is CVE-2023-27535?

Priority 55/100. Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities · curl vulnerabilities

Related CVEs

CVE-2023-27536 MEDIUM 5.9 UPGRADE MITIGATE An authentication bypass vulnerability exists libcurl <8.0.0 in the connection reuse feature which can reuse p
CVE-2023-27537 MEDIUM 5.9 DOWNGRADE MITIGATE A double free vulnerability exists in libcurl <8.0.0 when sharing HSTS data between separate "handles"

References

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