A use-after-free vulnerability in libcurl was found. libcurl works with easy handles using the type 'CURL *' that are objects the application creates using curl_easy_init(). They are the handles that are all each associated with a single transfer at a time. libcurl also has an internal struct that represents and holds most state that is related to a single connection. An easy handle can hold references to one or many such connection structs depending on the requested operations.
When using libcurl's multi interface, an application performs transfers by adding one or more easy handles to the multi handle and then it can drive all those transfers in parallel.
Due to a flaw, libcurl could leave a pointer to a freed connection struct dangling in an easy handle that was previously added to a multi handle when curl_multi_cleanup() is called with an easy handle still added to it. This does not seem to cause any notable harm if the handle is then closed properly.
However, if the easy handle would instead get used again with the easy interface and curl_easy_perform() to do another transfer, it would blindly use the connection struct pointer now pointing to freed memory.
An application could be made to allocate its own fake version of the connect struct, fill in some data and then have the curl_easy_perform() call do something that clearly was not intended by the original code.
Created curl tracking bugs for this issue:
Affects: fedora-all [bug 1363642]
Created mingw-curl tracking bugs for this issue:
Affects: fedora-all [bug 1363643]
Affects: epel-7 [bug 1363644]
curl-7.47.1-6.fc24 has been pushed to the Fedora 24 stable repository. If problems still persist, please make note of it in this bug report.
curl-7.43.0-8.fc23 has been pushed to the Fedora 23 stable repository. If problems still persist, please make note of it in this bug report.
This issue has been addressed in the following products:
Red Hat Software Collections for Red Hat Enterprise Linux 6
Red Hat Software Collections for Red Hat Enterprise Linux 7
Red Hat Software Collections for Red Hat Enterprise Linux 7.4 EUS
Red Hat Software Collections for Red Hat Enterprise Linux 7.5 EUS
Red Hat Software Collections for Red Hat Enterprise Linux 7.6 EUS
Via RHSA-2018:3558 https://access.redhat.com/errata/RHSA-2018:3558
The versions of `curl` as shipped with Red Hat Enterprise Linux 5, 6, and 7 are marked as "notaffected" because they did not include the vulnerable code, which was introduced in a later version of the package. Specifically, the struct field affected by this flaw was introduced in `curl` upstream version 7.32.0. The version of `curl` as shipped with Red Hat Enterprise Linux 7 is 7.29.0.
This flaw was introduced in upstream version 7.32.0 via the following commit:
More in detail, the affected field `easy_conn` was added in the SessionHandle struct in lib/urldata.h.
Only libcurl >= 7.32.0 to and including 7.50.0 are affected by this flaw.