When `CURLOPT_PINNEDPUBLICKEY` is configured alongside options that disable
standard peer verification (`CURLOPT_SSL_VERIFYPEER = 0` and
`CURLOPT_SSL_VERIFYHOST = 0`), libcurl fails to enforce public key pinning on
connections established without a presented server certificate. Bypassing the
pinning check under these disabled-verification conditions allows
unauthenticated connections to succeed when they should be rejected.
CVSS Score
7.5
EPSS Score
0.004
Published
2026-09-06
When libpsl support is enabled, libcurl fails to enforce the Public Suffix
List boundary check when processing a `Set-Cookie` header where the `Domain`
attribute explicitly matches an origin host that is itself a public suffix
(e.g., `Domain=co.uk` set by `co.uk`).
Instead of coercing it into a strict host-only cookie, libcurl saves the
cookie with wildcard domain scope (`.co.uk`). Consequently, the cookie is
inappropriately included in subsequent outbound requests or HTTP redirects to
arbitrary sibling subdomains under the same public suffix (e.g.,
`attacker.co.uk`).
CVSS Score
8.2
EPSS Score
0.004
Published
2026-09-06
A flaw in libcurl's handling of HTTP/2 Server Push streams, when the parent
handle is set to share connections with other handles, can lead to
use-after-free in the cleanup process.
CVSS Score
9.1
EPSS Score
0.006
Published
2026-09-06
When reusing a libcurl handle for sequential transfers driven by
environment-variable proxy configuration, libcurl fails to clear the proxy
authentication state between requests. Specifically, if the initial transfer
authenticates against `proxyA` using Digest auth, a subsequent transfer routed
through `proxyB` erroneously leaks the `Proxy-Authorization:` header intended
solely for `proxyA`.
CVSS Score
9.1
EPSS Score
0.005
Published
2026-07-03
libcurl would reuse a previously created connection even when some mTLS config
related option had been changed that should have prohibited reuse.
libcurl keeps previously used connections in a connection pool for subsequent
transfers to reuse if one of them matches the setup. However, some TLS
settings related to client certificates were left out from the configuration
match checks, making them match too easily. In particular options related to
the private key.
CVSS Score
7.5
EPSS Score
0.004
Published
2026-07-03
A vulnerability exists where a new transfer that uses STARTTLS to upgrade the
connection might reuse an existing live connection even though the TLS
configuration mismatches so it should not.
CVSS Score
8.1
EPSS Score
0.003
Published
2026-07-03
libcurl might in some circumstances reuse the wrong connection when asked to
do Negotiate-authenticated ones, even when they are set to use different
"services".
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 services.
CVSS Score
6.5
EPSS Score
0.004
Published
2026-07-03
A flaw in curl’s cookie parsing logic allows a malicious HTTP server to set
"super cookies" that bypass the Public Suffix List check. This enables an
attacker-controlled origin to inject cookies that curl subsequently scopes and
transmits to unrelated third-party domains.
CVSS Score
9.1
EPSS Score
0.007
Published
2026-07-03
Successfully using libcurl to do a transfer to a specific HTTP origin
(`hostA`) with **Digest** authentication and then changing the origin to a
different one (`hostB`) for a second transfer, reusing the same handle, makes
libcurl wrongly pass on the `Authorization:` header field meant for `hostA`,
to `hostB`.
CVSS Score
9.8
EPSS Score
0.007
Published
2026-07-03
Successfully using libcurl to do a transfer over a specific HTTP proxy
(`proxyA`) with **Digest** authentication and then changing the proxy host to
a second one (`proxyB`) for a second transfer, reusing the same handle, makes
libcurl wrongly pass on the `Proxy-Authorization:` header field meant for
`proxyA`, to `proxyB`.
CVSS Score
5.3
EPSS Score
0.005
Published
2026-05-13
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