CVE-2021-22901
HighCVSS 8.1Exploitation Probability (EPSS)
Very high risk99th percentile - higher than 99% of all known CVEs
Summary
curl versions 7.75.0 through 7.76.1 suffer from a use-after-free vulnerability resulting in already freed memory being used when a TLS 1.3 session ticket arrives over a connection. A malicious server can use this in rare unfortunate circumstances to potentially reach remote code execution in the client.
Risk Assessment
A malicious server can potentially execute arbitrary code on the client, potentially leading to client system compromise, data theft, or further attacks.
Recommendation
Immediately upgrade curl to version 7.77.0 or later, which contains the fix. Also monitor TLS 1.3 connections and limit trust in servers.
Other vulnerabilities in curl
See all- CVE-2022-27775High
An information disclosure vulnerability exists in curl versions 7.65.0 to 7.82.0 that allows reusing a connection using an IPv6 address with a different zone id.
- CVE-2022-22576High
An improper authentication vulnerability exists in curl versions 7.33.0 to 7.82.0 which might allow reuse of OAUTH2-authenticated connections without properly ensuring that the connection was authenticated with the same credentials. This affects SASL-enabled protocols: SMPTP(S), IMAP(S), POP3(S), and LDAP(S) (openldap only).
- CVE-2024-11053Low
When curl is asked to use a `.netrc` file for credentials and to follow HTTP redirects, it could leak the password used for the first host to the followed-to host under certain circumstances. This flaw only manifests if the netrc file has an entry matching the redirect target hostname.
- CVE-2024-9681Medium
When curl is asked to use HSTS, the expiry time for a subdomain might overwrite a parent domain's cache entry, making it end sooner or later than otherwise intended. This affects applications using HSTS and URLs with the insecure HTTP:// scheme.
- CVE-2024-8096Medium
When curl is told to use the Certificate Status Request TLS extension (OCSP stapling) to verify the server certificate, it might fail to detect some OCSP problems and wrongly consider the response as fine if the returned status reports another error than expected.
- CVE-2026-8926Critical
When curl uses a .netrc file for credentials and a URL with a username (without password) is specified, curl may wrongly retrieve and use the password of another user from .netrc for that host if no match exists for the specified user.
- CVE-2026-8925Critical
A double-free vulnerability has been found in the curl library's SASL authentication handling. The GSASL context is cleaned up twice without clearing the pointer, causing free() to be called on the same memory region twice.
- CVE-2026-8924Critical
A flaw in curl's cookie parsing logic allows a malicious HTTP server to set "super cookies" that bypass the Public Suffix List check, enabling injection of cookies that curl scopes and sends to unrelated third-party domains.
- CVE-2023-38545Critical
CVE-2023-38545 is a vulnerability related to heap buffer overflow during the SOCKS5 proxy handshake in curl. The issue arises when curl passes a hostname that is too long to the proxy, leading to incorrect data copying.
- CVE-2026-80255High
A Set-Cookie header using a tab (ASCII 9) instead of a space (ASCII 32) immediately before the Secure attribute causes curl to store the cookie without its Secure flag. The cookie might then wrongfully be sent over plaintext HTTP on subsequent requests to the same host.
Original NVD description (English source)
curl 7.75.0 through 7.76.1 suffers from a use-after-free vulnerability resulting in already freed memory being used when a TLS 1.3 session ticket arrives over a connection. A malicious server can use this in rare unfortunate circumstances to potentially reach remote code execution in the client. When libcurl at run-time sets up support for TLS 1.3 session tickets on a connection using OpenSSL, it stores pointers to the transfer in-memory object for later retrieval when a session ticket arrives. If the connection is used by multiple transfers (like with a reused HTTP/1.1 connection or multiplexed HTTP/2 connection) that first transfer object might be freed before the new session is established on that connection and then the function will access a memory buffer that might be freed. When using that memory, libcurl might even call a function pointer in the object, making it possible for a remote code execution if the server could somehow manage to get crafted memory content into the correct place in memory.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS