Internet Bug Bounty · Report #1912782
CVE-2023-27536: GSS delegation too eager connection re-use
Summary
CVE-2023-27536: GSS delegation too eager connection re-use
Project curl Security Advisory, March 20th 2023 - Permalink
VULNERABILITY
libcurl would reuse a previously created connection even when the GSS
delegation (CURLOPT_GSSAPI_DELEGATION) option had been changed that could
have changed the user's permissions in a second transfer.
libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if one of them matches the setup. However, this GSS delegation setting was left out from the configuration match checks, making them match too easily, affecting krb5/kerberos/negotiate/GSSAPI transfers.
We are not aware of any exploit of this flaw.
INFO
CVE-2023-27536 was introduced in commit ebf42c4be76df4, shipped in curl 7.22.0.
CWE-305: Authentication Bypass by Primary Weakness
Severity: Low
AFFECTED VERSIONS
- Affected versions: curl 7.22.0 to and including 7.88.1
- Not affected versions: curl < 7.22.0 and curl >= 8.0.0
libcurl is used by many applications, but not always advertised as such!
THE SOLUTION
RECOMMENDATIONS
A - Upgrade curl to version 8.0.0
B - Apply the patch to your local version
C - Do not use the CURLOPT_GSSAPI_DELEGATION option
How it was found
libcurl would reuse a previously created connection even when the GSS delegation (CURLOPT_GSSAPI_DELEGATION) option had been changed that could have changed the user's permissions in a second transfer.
libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if one of them matches the setup. However, this GSS delegation setting was left out from the configuration match checks, making them match too easily, affecting krb5/kerberos/negotiate/GSSAPI transfers.
Hackerone report
#1895135
Impact
Existing connection that was established via more lax delegation will be reused for connection that should not succeed due to more restrictive delegation requested.