CVE-2022-32205

Set-Cookie denial of service

Project curl Security Advisory, June 27th 2022 - Permalink

VULNERABILITY

A malicious server can serve excessive amounts of Set-Cookie: headers in a HTTP response to curl and curl stores all of them. A sufficiently large amount of (big) cookies make subsequent HTTP requests to this, or other servers to which the cookies match, create requests that become larger than the threshold that curl uses internally to avoid sending crazy large requests (1048576 bytes) and instead returns an error.

This denial state might remain for as long as the same cookies are kept, match and have not expired. Due to cookie matching rules, a server on foo.example.com can set cookies that also would match for bar.example.com, making it it possible for a "sister server" to effectively cause a denial of service for a sibling site on the same second level domain using this method.

INFO

CVE-2022-32205 was introduced in commit ed35d6590e72c23c, shipped in curl 7.71.0 with the introduction of the "dynbuf" internally. Before this change, curl had no limit in how large HTTP request it could generate.

CWE-770: Allocation of Resources Without Limits or Throttling

Severity: Low

AFFECTED VERSIONS

• Affected versions: curl 7.71.0 to and including 7.83.1
• Not affected versions: curl < 7.71.0 and curl >= 7.84.0
• Introduced-in: https://github.com/curl/curl/commit/ed35d6590e72c23c

libcurl is used by many applications, but not always advertised as such!

SOLUTION

We introduce several new limits and thresholds for cookies:

• Send no more than 150 cookies per request

• Cap the max length used for an outgoing Cookie: header to 8K

• Cap the max number of accepted Set-Cookie: header fields to 50

• Fixed-in: https://github.com/curl/curl/commit/48d7064a49148f0394

RECOMMENDATIONS

A - Upgrade curl to version 7.84.0

B - Apply the patch to your local version

C - Do not use cookies

TIMELINE

This issue was reported to the curl project on May 13, 2022. We contacted distros@openwall on June 20.

libcurl 7.84.0 was released on June 27 2022, coordinated with the publication of this advisory.

CREDITS

• Reported-by: Harry Sintonen
• Patched-by: Daniel Stenberg

Thanks a lot!