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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.0966 HVM soft-reset crashes toolstack 19 March 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: Linux variants Xen Impact/Access: Denial of Service -- Unknown/Unspecified Resolution: Patch/Upgrade CVE Names: CVE-2021-28687 Original Bulletin: http://xenbits.xen.org/xsa/advisory-368.html - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2021-28687 / XSA-368 version 3 HVM soft-reset crashes toolstack UPDATES IN VERSION 3 ==================== CVE assigned. ISSUE DESCRIPTION ================= libxl requires all data structures passed across its public interface to be initialized before use and disposed of afterwards by calling a specific set of functions. Many internal data structures also require this initialize / dispose discipline, but not all of them. When the "soft reset" feature was implemented, the libxl__domain_suspend_state structure didn't require any initialization or disposal. At some point later, an initialization function was introduced for the structure; but the "soft reset" path wasn't refactored to call the initialization function. When a guest nwo initiates a "soft reboot", uninitialized data structure leads to an assert() when later code finds the structure in an unexpected state. The effect of this is to crash the process monitoring the guest. How this affects the system depends on the structure of the toolstack. For xl, this will have no security-relevant effect: every VM has its own independent monitoring process, which contains no state. The domain in question will hang in a crashed state, but can be destroyed by `xl destroy` just like any other non-cooperating domain. For daemon-based toolstacks linked against libxl, such as libvirt, this will crash the toolstack, losing the state of any in-progress operations (localized DoS), and preventing further administrator operations unless the daemon is configured to restart automatically (system-wide DoS). If crashes "leak" resources, then repeated crashes could use up resources, also causing a system-wide DoS. IMPACT ====== A malicious guest can crash the management daemon, leading to at least a localized, possibly system-wide denial-of-service. VULNERABLE SYSTEMS ================== Only Xen versions 4.12 through 4.14 are affected. Earlier versions are not affected. The issue affects only systems with a guest monitoring process, which is linked against libxl, and which is important other than simply for the functioning of one particular guest. libvirt is one common toolstack affected. Systems using the `xl` command-line tool should generally suffer no security-relevant effects. The xapi toolstack does not currently link against libxl, and so is not affected. MITIGATION ========== Ensuring that any management daemons are restarted automatically after a crash will partially mitigate the issue. CREDITS ======= This issue was discovered by Olaf Hering. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. Note that patches for released versions are generally prepared to apply to the stable branches, and may not apply cleanly to the most recent release tarball. Downstreams are encouraged to update to the tip of the stable branch before applying these patches. xsa368.patch xen-unstable xsa368-4.14.patch Xen 4.14.x xsa368-4.13.patch Xen 4.13.x - Xen 4.12.x $ sha256sum xsa368* e80f33c3ce45372fef7bd91ec71b2b66e557176b79f9771872ce111bfff34150 xsa368.meta b82f2b110514cdf47a2688913ad5af68b01050751d56705a15ddf9a970b6fa0d xsa368.patch 636df70ae5eaf00b50ef0b5ac219a2aeda771c66833fae88e7ee43b18ae889f4 xsa368-4.13.patch 55bbe59c75b69f493e364dfcf6cdbc7db4acd32dbf0b4d2466815b7c1f1823ce xsa368-4.14.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches and/or mitigations described above (or others which are substantially similar) is permitted during the embargo, even on public-facing systems with untrusted guest users and administrators. But: Distribution of updated software is prohibited (except to other members of the predisclosure list). Predisclosure list members who wish to deploy significantly different patches and/or mitigations, please contact the Xen Project Security Team. (Note: this during-embargo deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable. This is to enable the community to have oversight of the Xen Project Security Team's decisionmaking.) For more information about permissible uses of embargoed information, consult the Xen Project community's agreed Security Policy: http://www.xenproject.org/security-policy.html - -----BEGIN PGP SIGNATURE----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAmBTXAAMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZdgcH/RTW41tLPh8KHJ+82qefaI2EUBK3nmNnR5hnye3c 9GPP/QB7QdHp+JSIRTAZxOayBQeFEcYSX/5VxDypIiqT02wHS9hDr3jcpOfGLcdt MiN9kB3vYqe353Lask0mN7AX3J5v3wvrYzBRx9ccaYcX/Jcubrx6Jy5laQSYpTUu 4GCeLZQ2tHI8N3ZHiKI7YUyxmn9vKgvFil1gyuk8L5x6npnW4ixdWF0MRyHe7wbS dbZbug0g6bbJbs4CFZbm1CbQjGGOwznfT8z9ppmgPdi+33X+Cimz3wlbpXeJKpZk /nJObobdPGk7ClChvUjntv0oaZ+2zFoUoe3Yc08aa+B29e8= =Dehk - -----END PGP SIGNATURE----- - --------------------------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. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. 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 iQIVAwUBYFP2TONLKJtyKPYoAQgPTQ//UGkS8IoLUJBvu2D2ssVBL1bfQqXfxm8i 4xEZjsJfGm1ZS01IuIN1o7XZXY7Gckzmv60cyFdFXatBbeJIhsnh2ufDVQdwwfp9 1ZsjoC5NjcIsKMi05upcr4zG1scjSLIqwRP/+Cy1WEyYkbNjMFr3N6+9KlbWi8J/ /yddgLQ5Ro6N5Ktf/u88VHS/BkZrx1VQyFyTnVZ+8LUfe/TBukUg4jrV2JVjY0gE jXBubp1bIjzQqBVnKFFiT0zo17abSyRu6Vd9Rr/47ECnL8FvCC6kpT+wXUAjZ4XZ S/fRM0LDcbfixhXhQwGwzdBjx11gOzIqaNVoaUbyfhnsyE+9FvmGArvmWQ50HHtD Lu8qNe1mK4DUWrMNoN0TkAY57KRe0vvsdXj6pCwv4fBcHKYWaCsmo4sONBkuhDMz 0LpiftA68OKqKSg2UlXzBM7bFrWVzMAaAaeG0n8ne8JisqmKptGqQ0jdt1jLEyeW q8g3l+IOFw1n3ckzEYNDqeURSJ+IyIj8HFM7vDN1WSPseGTx8IXxWDpe4v+w9c/r t4akv0oLb1S+hF8EGp/3Z8euGsgpmt3+IZ/GOZjY7i5SfUOF6fxvnkisXz1qJPF0 LWBGrvQ7bLdiGVf0bFHdwsHhE9Ox8Zj7NPqz1GjOOGzyzCToY8Gl9clQ45is98dc ARQIOglYbDg= =nIh2 -----END PGP SIGNATURE-----