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CVE-2023-27537

curl: HSTS double-free

A double free vulnerability exists in libcurl <8.0.0 when sharing HSTS data between separate "handles". This sharing was introduced without considerations for do this sharing across separate threads but there was no indication of this fact in the documentation. Due to missing mutexes or thread locks, two threads sharing the same HSTS data could end up doing a double-free or use-after-free.

CVSS 3.1 · 5.9 Medium EPSS 1.9% KEV · Not listed
Vendors
Broadcom Haxx Netapp and 1 more
Products
Brocade Fabric Operating System Firmware Libcurl Active Iq Unified Manager and 10 more
CVE-2025-0725

gzip integer overflow

When libcurl is asked to perform automatic gzip decompression of content-encoded HTTP responses with the `CURLOPT_ACCEPT_ENCODING` option, **using zlib 1.2.0.3 or older**, an attacker-controlled integer overflow would make libcurl perform a buffer overflow.

CVSS 3.1 · 7.3 High EPSS 1.8% KEV · Not listed
Vendors
Haxx Netapp Zlib
Products
Curl Libcurl Hci Baseboard Management Controller and 9 more
CVE-2025-0665

eventfd double close

libcurl would wrongly close the same eventfd file descriptor twice when taking down a connection channel after having completed a threaded name resolve.

CVSS 3.1 · 7 High EPSS 1.3% KEV · Not listed
Vendors
Curl Haxx Netapp
Products
Curl Libcurl Curl and 12 more
CVE-2024-7264

ASN.1 date parser overread

libcurl's ASN1 parser code has the `GTime2str()` function, used for parsing an ASN.1 Generalized Time field. If given an syntactically incorrect field, the parser might end up using -1 for the length of the *time fraction*, leading to a `strlen()` getting performed on a pointer to a heap buffer area that is not (purposely) null terminated. This flaw most likely leads to a crash, but can also lead to heap contents getting returned to the application when [CURLINFO_CERTINFO](https://curl.se/libcurl/c/CURLINFO_CERTINFO.html) is used.

CVSS 3.1 · 6.3 Medium EPSS 20.2% KEV · Not listed
Vendors
Haxx Redhat
Products
Libcurl Enterprise Linux Service Mesh
CVE-2024-2466

TLS certificate check bypass with mbedTLS

libcurl did not check the server certificate of TLS connections done to a host specified as an IP address, when built to use mbedTLS. libcurl would wrongly avoid using the set hostname function when the specified hostname was given as an IP address, therefore completely skipping the certificate check. This affects all uses of TLS protocols (HTTPS, FTPS, IMAPS, POPS3, SMTPS, etc).

CVSS 3.1 · 6.5 Medium EPSS 1.5% KEV · Not listed
Vendors
Apple Curl Haxx and 2 more
Products
Macos Libcurl Curl and 11 more
CVE-2023-27538

curl: SSH connection too eager reuse still

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 leading to the reuse of an inappropriate connection.

CVSS 3.1 · 7.7 High EPSS 1.5% KEV · Not listed
Vendors
Broadcom Debian Fedoraproject and 4 more
Products
Brocade Fabric Operating System Firmware Debian Linux Fedora and 13 more
CVE-2023-27536

curl: GSS delegation too eager connection re-use

An authentication bypass vulnerability exists libcurl <8.0.0 in the connection reuse feature which can reuse previously established connections with incorrect user permissions due to a failure to check for changes in the CURLOPT_GSSAPI_DELEGATION option. This vulnerability affects krb5/kerberos/negotiate/GSSAPI transfers and could potentially result in unauthorized access to sensitive information. The safest option is to not reuse connections if the CURLOPT_GSSAPI_DELEGATION option has been changed.

CVSS 3.1 · 5.9 Medium EPSS 1.8% KEV · Not listed
Vendors
Debian Fedoraproject Haxx and 3 more
Products
Debian Linux Fedora Libcurl and 13 more
CVE-2023-27535

curl: FTP too eager connection reuse

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 configuration match checks, causing them to match too easily. This could lead to libcurl using the wrong credentials when performing a transfer, potentially allowing unauthorized access to sensitive information.

CVSS 3.1 · 5.9 Medium EPSS 1.8% KEV · Not listed
Vendors
Debian Fedoraproject Haxx and 3 more
Products
Debian Linux Fedora Libcurl and 13 more
CVE-2021-22945

curl: use-after-free and double-free in MQTT sending

When sending data to an MQTT server, libcurl <= 7.73.0 and 7.78.0 could in some circumstances erroneously keep a pointer to an already freed memory area and both use that again in a subsequent call to send data and also free it *again*.

CVSS 3.1 · 9.1 Critical EPSS 6.7% KEV · Not listed
Vendors
Apple Debian Fedoraproject and 5 more
Products
Macos Debian Linux Fedora and 22 more
CVE-2021-22924

curl: Bad connection reuse due to flawed path name checks

libcurl keeps previously used connections in a connection pool for subsequenttransfers to reuse, if one of them matches the setup.Due to errors in the logic, the config matching function did not take 'issuercert' into account and it compared the involved paths *case insensitively*,which could lead to libcurl reusing wrong connections.File paths are, or can be, case sensitive on many systems but not all, and caneven vary depending on used file systems.The comparison also didn't include the 'issuer cert' which a transfer can setto qualify how to verify the server certificate.

CVSS 3.1 · 3.7 Low EPSS 6.3% KEV · Not listed
Vendors
Debian Fedoraproject Haxx and 5 more
Products
Debian Linux Fedora Libcurl and 52 more
CVE-2021-22890

curl: TLS 1.3 session ticket mix-up with HTTPS proxy host

curl 7.63.0 to and including 7.75.0 includes vulnerability that allows a malicious HTTPS proxy to MITM a connection due to bad handling of TLS 1.3 session tickets. When using a HTTPS proxy and TLS 1.3, libcurl can confuse session tickets arriving from the HTTPS proxy but work as if they arrived from the remote server and then wrongly "short-cut" the host handshake. When confusing the tickets, a HTTPS proxy can trick libcurl to use the wrong session ticket resume for the host and thereby circumvent the server TLS certificate check and make a MITM attack to be possible to perform unnoticed. Note that such a malicious HTTPS proxy needs to provide a certificate that curl will accept for the MITMed server for an attack to work - unless curl has been told to ignore the server certificate check.

CVSS 3.1 · 4.3 Medium EPSS 3.1% KEV · Not listed
Vendors
Broadcom Debian Fedoraproject and 6 more
Products
Fabric Operating System Debian Linux Fedora and 9 more
CVE-2021-22876

curl: Leak of authentication credentials in URL via automatic Referer

curl 7.1.1 to and including 7.75.0 is vulnerable to an "Exposure of Private Personal Information to an Unauthorized Actor" by leaking credentials in the HTTP Referer: header. libcurl does not strip off user credentials from the URL when automatically populating the Referer: HTTP request header field in outgoing HTTP requests, and therefore risks leaking sensitive data to the server that is the target of the second HTTP request.

CVSS 3.1 · 5.3 Medium EPSS 5.3% KEV · Not listed
Vendors
Broadcom Debian Fedoraproject and 6 more
Products
Fabric Operating System Debian Linux Fedora and 12 more
CVE-2020-8286

curl: Inferior OCSP verification

curl 7.41.0 through 7.73.0 is vulnerable to an improper check for certificate revocation due to insufficient verification of the OCSP response.

CVSS 3.1 · 7.5 High EPSS 4.6% KEV · Not listed
Vendors
Apple Debian Fedoraproject and 6 more
Products
Mac Os X Macos Debian Linux and 19 more
CVE-2020-8285

curl: Malicious FTP server can trigger stack overflow when CURLOPT_CHUNK_BGN_FUNCTION is used

curl 7.21.0 to and including 7.73.0 is vulnerable to uncontrolled recursion due to a stack overflow issue in FTP wildcard match parsing.

CVSS 3.1 · 7.5 High EPSS 9.8% KEV · Not listed
Vendors
Apple Debian Fedoraproject and 7 more
Products
Mac Os X Macos Debian Linux and 29 more
CVE-2026-6429

netrc credential leak with reused proxy connection

When asked to both use a `.netrc` file for credentials and to follow HTTP redirects, libcurl could leak the password used for the first host to the followed-to host under certain circumstances.

CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
Vendors
Curl Haxx
Products
Libcurl Curl
CVE-2026-5773

wrong reuse of SMB connection

libcurl might in some circumstances reuse the wrong connection for SMB(S) transfers. libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead. When reusing a connection a range of criteria must be met. Due to a logical error in the code, a network transfer operation that was requested by an application could wrongfully reuse an existing SMB connection to the same server that was using a different "share" than the new subsequent transfer should. This could in unlucky situations lead to the download of the wrong file or the upload of a file to the wrong place. When this happens, the same credentials are used and the server name is the same.

CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Vendors
Curl Haxx
Products
Libcurl Curl
CVE-2026-5545

wrong reuse of HTTP Negotiate connection

libcurl might in some circumstances reuse the wrong connection when asked to do an authenticated HTTP(S) request after a Negotiate-authenticated one, when both use the same host. libcurl features a pool of recent connections so that subsequent requests can reuse an existing connection to avoid overhead. When reusing a connection a range of criteria must be met. Due to a logical error in the code, a request that was issued by an application could wrongfully reuse an existing connection to the same server that was authenticated using different credentials. An application that first uses Negotiate authentication to a server with `user1:password1` and then does another operation to the same server asking for any authentication method but for `user2:password2` (while the previous connection is still alive) - the second request gets confused and wrongly reuses the same connection and sends the new request over that connection thinking it uses a mix of user1's and user2's credentials when it is in fact still using the connection authenticated for user1...

CVSS 3.1 · 6.5 Medium EPSS < 1% KEV · Not listed
Vendors
Curl Haxx
Products
Libcurl Curl
CVE-2026-6276

stale custom cookie host causes cookie leak

Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.

CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
Vendors
Curl Haxx
Products
Libcurl Curl