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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.1816 Shibboleth Service Provider Security Advisory 27 May 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Shibboleth SP Publisher: Shibboleth Operating System: Windows UNIX variants (UNIX, Linux, OSX) Impact/Access: Execute Arbitrary Code/Commands -- Remote/Unauthenticated Denial of Service -- Remote/Unauthenticated Resolution: Patch/Upgrade CVE Names: CVE-2021-22901 Original Bulletin: https://curl.se/docs/CVE-2021-22901.html - --------------------------BEGIN INCLUDED TEXT-------------------- TLS session caching disaster Project curl Security Advisory, May 26th 2021 - Permalink VULNERABILITY libcurl can be tricked into using already freed memory when a new TLS session is negotiated or a client certificate is requested on an existing connection. For example, this can happen when a TLS server requests a client certificate on a connection that was established without one. A malicious server can use this in rare unfortunate circumstances to potentially reach remote code execution in the client. OpenSSL can declare a "new session" for different reasons, including the initial TLS handshake completion, TLS 1.2 (or earlier) renegotiation, or TLS 1.3 client certificate requests. When libcurl at run-time sets up support for session ID caching on a connection using OpenSSL, it stores pointers to the transfer in-memory object for later retrieval when OpenSSL considers a new session to be established. However, 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. We are not aware of any exploit of this flaw. INFO The flaw can only happen in libcurl built to use OpenSSL (or one of its forks). This flaw has existed in curl since commit a304051620b92 in libcurl 7.75.0, released on February 3, 2021. The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2021-22901 to this issue. CWE-416: Use After Free Severity: High Steps to remote code execution 1. libcurl built to use OpenSSL (BoringSSL and libressl work the same) 2. A multi interface using application 3. One of the following: o create and use a first easy handle to do HTTP/1.1 over TLS to a malicious server o free that easy handle with curl_easy_cleanup() o create and use a second easy handle to do HTTP/1.1 over TLS with to the same server such that the TLS connection is reused or o more than one concurrent easy handle created that do HTTP/2 over a TLS connection to a malicious server, o the first easy handle to use the connection must be freed with curl_easy_cleanup() o at least one easy handle remaining in use of the same connection 4. The attacking server needs to figure out heap address details in order to know what payload contents to provide 5. The necessary exact memory address in the heap gets populated by memory contents controlled by the server 6. The attacker starts a new handshake (on TLS 1.2 or earlier), or sends a TLS 1.3 client certificate request, or otherwise triggers OpenSSL to consider a new session to be established For a remote code execution, the client needs to perform (potentially many) more transfers (and thus have more easy handles) to allow the server to place crafted contents into heap memory. Instead of remote code execution, the client could instead crash or otherwise experience undefined behaviour. AFFECTED VERSIONS o Affected versions: curl 7.75.0 to and including 7.76.1 o Not affected versions: curl < 7.75.0 and curl >= 7.77.0 Also note that libcurl is used by many applications, and not always advertised as such. THE SOLUTION When the transfer is detached from the connection, it clears the association to it from the session ID cache logic. A fix for CVE-2021-22901 RECOMMENDATIONS A - Upgrade curl to version 7.77.0 B - Apply the patch to your local version C - Build libcurl to use another TLS backend TIMELINE This issue was reported to the curl project on April 29, 2021. This advisory was posted on May 26, 2021. CREDITS This issue was reported by Harry Sintonen. Patched by Harry Sintonen and Daniel Stenberg. Help and research by Brad Spencer. Thanks a lot! - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. 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If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBYK8DIeNLKJtyKPYoAQg6qQ//bv6wiRatlPLPJQG7lMTPHgDL5WIqOvcO 2//8S+6jrtVqWV6jkx+N0mkCVyLOHDdFuK9ao1gnWvakpIjYb9C0CfZFT+Ng31gD d47eRvGO9lNu84gicaJVWoWUAZCKcg2X1uFboDYY2Q8h/EpLpQAR57koNFoo0jCx xfbpj2r3TIcNOOFyAZKZ7m0AI5+NNY80rWClz4v4Ann0hcH3djinoaAxg0fzjso3 Vsih4xzL/68ZCghJ3Mk4HO2Lzi1UrQXg30y+lLLn02yIeGrC8q1IcRuq6HZBOXMr oJAzl146J+FHbkl9XbiK2ta4okll8zuT6M01JjE/pejKfzi5cRdoxR5Le9ZWpP/+ EV1MjYNTqILD3kV5KnmW8/bIuaysY4dOCzjJoBukAszkjrsLQlemdUW/A/an+SBD c5fmS8K7mpFoCuzavq4qLT/3o4B8EvxOrTFRyPbJJe5jFdP3VKSUyeOEjy0y8ERp ucziZq9J6HQXU/0djyyLykRBc4Nebvh27Cgz4Y9a7LvFZ4Qf/myzWYiQPvpt1QS9 6HA2h2YTumGlilMmlsGNbjaoklxGNIlOgmxUujxy8B4k8wmhQfoj/JX/ekzMnCOD 0jQdIx5d0IVUASKccLZITCskCPhzvhtGTDjL2nvKrOijizGUATF9EUwjx/N1cIj7 dstnOnh5Htg= =eaTa -----END PGP SIGNATURE-----