curl libcURL up to 8.20.0 Certificate information disclosure

Summaryinfo

A vulnerability identified as problematic has been detected in curl libcURL up to 8.20.0. This impacts an unknown function of the component Certificate Handler. Performing a manipulation results in information disclosure. This vulnerability is reported as CVE-2026-9545. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as problematic, was found in curl libcURL up to 8.20.0. This affects some unknown functionality of the component Certificate Handler. The manipulation with an unknown input leads to a information disclosure vulnerability. CWE is classifying the issue as CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. This is going to have an impact on confidentiality. The summary by CVE is:

In this scenario, libcurl first uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate. When libcurl returns to the hostname the second time with a cached SSL session (`CURLOPT_SSL_SESSIONID_CACHE` is not disabled) and early data enabled (the `CURLSSLOPT_EARLYDATA` bit is set in `CURLOPT_SSL_OPTIONS`), libcurl might send off the second request's bytes on that new connection *before* enforcing the certificate verification failure. Potentially leaking sensitive information.

The advisory is shared at curl.se. This vulnerability is uniquely identified as CVE-2026-9545 since 05/26/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1592 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 326237 (libcurl 8.11.0 < 8.21.0 HTTP/3 Early Data Information Disclosure (CVE-2026-9545)), which helps to determine the existence of the flaw in a target environment.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the databases at Tenable (326237), EUVD (EUVD-2026-41493) and CERT Bund (WID-SEC-2026-2052). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

• Red Hat Enterprise Linux
• Ubuntu Linux
• Open Source cURL

Productinfo

Type

• Network Utility Software

Vendor

• curl

Name

• libcURL

Version

• 8.0
• 8.1
• 8.2
• 8.3
• 8.4
• 8.5
• 8.6
• 8.7
• 8.8
• 8.9
• 8.10
• 8.11
• 8.11.0
• 8.11.1
• 8.12
• 8.12.0
• 8.12.1
• 8.13
• 8.13.0
• 8.14
• 8.14.0
• 8.14.1
• 8.15
• 8.15.0
• 8.16
• 8.16.0
• 8.17
• 8.17.0
• 8.18
• 8.18.0
• 8.19
• 8.19.0
• 8.20.0

License

• open-source

CPE 2.3info

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CPE 2.2info

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CVSSv3info

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Exploitinginfo

Threat Intelligenceinfo

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Timelineinfo

Sourcesinfo

Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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