CVE-2026-9547
HighCVSS 7.4Exploitation Probability (EPSS)
Low risk30th percentile - higher than 30% of all known CVEs
Summary
A vulnerability in libcurl allows accepting an untrusted server during SCP or SFTP transfers when using the CURLOPT_SSH_KEYFUNCTION callback. The server can present a host key type different from the one recorded in the known_hosts file, and the callback mechanism fails to enforce rejection, allowing the connection to succeed without warning.
Risk Assessment
The risk involves a potential man-in-the-middle attack where an attacker can impersonate a trusted server, leading to interception or modification of transmitted data.
Recommendation
It is recommended to immediately update libcurl to a version that fixes this vulnerability. Until updated, avoid using CURLOPT_SSH_KEYFUNCTION with SCP and SFTP protocols or manually verify host keys.
Other vulnerabilities in libcurl
See all- CVE-2022-27782High
libcurl has an issue with reusing previously created connections even when TLS or SSH-related options have been changed that should prohibit reuse. Several TLS and SSH settings were left out from the configuration match checks, making them match too easily.
- CVE-2022-27781High
libcurl provides the `CURLOPT_CERTINFO` option to allow applications to request details about a server's certificate chain. Due to an erroneous function, a malicious server could make libcurl built with NSS get stuck in a never-ending busy-loop when trying to retrieve that information.
- CVE-2021-22926High
libcurl-using applications can request a specific client certificate to be used in a transfer. When built with the macOS native TLS library Secure Transport, a malicious user can trick the application into using a file-based certificate instead of the intended one, leading to the wrong client certificate being sent in the TLS handshake.
- CVE-2017-1000254High
libcurl may read outside of a heap allocated buffer when doing FTP. A flaw in the string parser for the directory name may lead to a missing NUL byte at the end of the buffer, resulting in the potential to read data beyond the allocated memory area.
- CVE-2016-5421High
Use-after-free vulnerability in libcurl before version 7.50.1 allows attackers to control which connection is used or possibly have unspecified other impact via unknown vectors.
- CVE-2016-0755High
The ConnectionExists function in lib/url.c in libcurl before version 7.47.0 does not properly re-use NTLM-authenticated proxy connections, which might allow remote attackers to authenticate as other users via a request.
- CVE-2024-6874Medium
The curl_url_get() function in libcurl offers punycode conversions to and from IDN. When converting a name that is exactly 256 bytes, libcurl reads outside a stack-based buffer when built with the macidn IDN backend.
- CVE-2024-2398Medium
A vulnerability in the libcurl library causes a memory leak when handling HTTP/2 server push. When an application allows server push and the number of headers exceeds the limit of 1000, libcurl aborts the push but fails to free previously allocated headers.
- CVE-2025-4947Medium
libcurl accidentally skips certificate verification for QUIC connections when connecting to a host specified as an IP address in the URL. Therefore, it does not detect impostors or man-in-the-middle attacks.
- CVE-2024-6197High
libcurl's ASN1 parser has this utf8asn1str() function used for parsing an ASN.1 UTF-8 string. It can detect an invalid field and return error. Unfortunately, when doing so it also invokes `free()` on a 4 byte local stack buffer. Most modern malloc implementations detect this error and immediately abort.
Original NVD description (English source)
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 the connection to succeed without warning and risking a potential man-in-the-middle attack.