CVE-2021-22901

CVE-2021-22901 is a high-severity vulnerability in Haxx Curl with a CVSS 3.x base score of 8.1. Its EPSS exploit-prediction score of 60% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-416.

Key facts

Description

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.

Frequently asked questions

What is CVE-2021-22901?
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.
How severe is CVE-2021-22901?
CVE-2021-22901 has a CVSS 3.x base score of 8.1, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-22901 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 60% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-22901?
CVE-2021-22901 primarily affects Haxx Curl. In total, 29 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-22901?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-22901 published?
CVE-2021-22901 was published on 2021-06-11 and last updated on 2026-06-17.

References

Affected products (29)

More vulnerabilities in Haxx Curl

All CVEs affecting Haxx Curl →

Other CWE-416 (Use After Free) vulnerabilities

Browse all CWE-416 (Use After Free) vulnerabilities →