CVE-2023-27538: An authentication bypass vulnerability exists in libcurl prior to v8.0.0 where it reuses a previously establis

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MEDIUM 5.5WATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2023-27538 is a medium-severity flaw (CVSS 5.5) 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 prior to v8.0.0 where it reuses a previously established SSH connection despite the fact that an SSH option was modified, which should have prevented reuse. libcurl maintains a pool of previously used connections to reuse them for subsequent transfers if the configurations match. However, two SSH settings were omitted from the configuration check, allowing them to match easily, potentially

Why this priority

Public exploit reference
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.5% (top 27%)
CISA exploited list	No
Weakness	CWE-305, CWE-287
Published	2023-03-30
Last modified	2026-10-14

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

Last updated 2026-10-14 · 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
2026-10-14 23:17 UTCUpdated Record last modified

haxx libcurl UPGRADE

Affected: >= 7.16.1 and < 8.0.0

Fixed in: 8.0.0

Safe to downgrade to: a release before 7.16.1

1. Check installed version

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

2. UPGRADE to 8.0.0 (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 7.16.1 (Debian / Ubuntu)

apt-cache madison libcurl sudo apt install libcurl=<VERSION_BEFORE_7.16.1> 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_7.16.1> 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 clustered data ontap DOWNGRADE

Affected: 9.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.0

1. Check installed version

apt-cache policy clustered-data-ontap || rpm -q clustered-data-ontap || clustered-data-ontap --version

2. No fixed release: DOWNGRADE to a release before 9.0 (Debian / Ubuntu)

apt-cache madison clustered-data-ontap sudo apt install clustered-data-ontap=<VERSION_BEFORE_9.0> sudo apt-mark hold clustered-data-ontap

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list clustered-data-ontap sudo dnf downgrade clustered-data-ontap-<VERSION_BEFORE_9.0> sudo dnf versionlock add clustered-data-ontap

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.

broadcom brocade fabric operating system 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.

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-2023-27538?

libcurl: upgrade to 8.0.0; 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-2023-27538 being exploited?

CVE-2023-27538 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-2023-27538 affect?

CVE-2023-27538 affects libcurl, fedora, debian linux. Severity is medium (CVSS 5.5). An authentication bypass vulnerability exists in libcurl prior to v8.0.0 where it reuses a previously established SSH connection despite the fact that an SSH option was modified, which should have prevented reuse. libcurl maintains a pool o

How urgent is CVE-2023-27538?

Priority 48/100. Public exploit reference; On your watchlist

Software pages

Debian vulnerabilities · curl vulnerabilities

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References

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