CVE-2026-9547: When a libcurl-based application performs transfers via `SCP://` or `SFTP://` and utilizes the `CURLOPT_SSH_KE

This week

HIGH 7.4REMOTEUPGRADE

CVE-2026-9547 is a high-severity flaw (CVSS 7.4) affecting curl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

When a libcurl-based application performs transfers via `SCP://` or `SFTP://` and utilizes the `CURLOPT_SSH_KEYFUNCTION` callback, it may silently accept an untrusted server. This vulnerability occurs when a server presents a host key type that does not match the specific key type already recorded for that host in the `known_hosts` file. Instead of rejecting the mismatch, the callback mechanism fails to properly enforce the restriction, allowing

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.4 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 70%)
CISA exploited list	No
Weakness	CWE-297
Published	2026-07-03
Last modified	2026-09-15

Publisher (CNA): curl · Vendor: haxx

Last updated 2026-09-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-03 07:16 UTCPublished CVE record published
2026-09-15 07:16 UTCUpdated Record last modified

haxx curl UPGRADE

Affected: >= 7.69.0 and < 8.21.0

Fixed in: 8.21.0

Safe to downgrade to: a release before 7.69.0

1. Check installed version

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

2. UPGRADE to 8.21.0 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade curl

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 7.69.0 (Debian / Ubuntu)

apt-cache madison curl sudo apt install curl=<VERSION_BEFORE_7.69.0> sudo apt-mark hold curl

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

dnf --showduplicates list curl sudo dnf downgrade curl-<VERSION_BEFORE_7.69.0> sudo dnf versionlock add curl

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.

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-2026-9547?

curl: upgrade to 8.21.0. Exact commands for each OS are on this page.

Is CVE-2026-9547 being exploited?

CVE-2026-9547 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-2026-9547 affect?

CVE-2026-9547 affects curl. Severity is high (CVSS 7.4). When a libcurl-based application performs transfers via `SCP://` or `SFTP://` and utilizes the `CURLOPT_SSH_KEYFUNCTION` callback, it may silently accept an untrusted server. This vulnerability occurs when a server presents a host key type

How urgent is CVE-2026-9547?

Priority 43/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

curl vulnerabilities

Related CVEs

CVE-2023-23915 MEDIUM 6.5 UPGRADE MITIGATE A cleartext transmission of sensitive information vulnerability exists in curl <v7.88.0 that could cause HSTS
CVE-2023-27534 HIGH 8.8 UPGRADE MITIGATE A path traversal vulnerability exists in curl <8.0.0 SFTP implementation causes the tilde (~) character to be
CVE-2023-28319 HIGH 7.5 UPGRADE UPGRADE A use after free vulnerability exists in curl <v8.1.0 in the way libcurl offers a feature to verify an SSH ser
CVE-2023-28321 MEDIUM 5.9 UPGRADE MITIGATE An improper certificate validation vulnerability exists in curl <v8.1.0 in the way it supports matching of wil
CVE-2022-43552 MEDIUM 5.9 UPGRADE UPGRADE A use after free vulnerability exists in curl <7.87.0

References

← Back to latest CVEs