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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2019.4061 VCPUOP_initialise DoS 1 November 2019 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: Xen Impact/Access: Denial of Service -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2019-18420 Original Bulletin: http://xenbits.xen.org/xsa/advisory-296.html - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2019-18420 / XSA-296 version 4 VCPUOP_initialise DoS UPDATES IN VERSION 4 ==================== Public release. ISSUE DESCRIPTION ================= hypercall_create_continuation() is a variadic function which uses a printf-like format string to interpret its parameters. Error handling for a bad format character was done using BUG(), which crashes Xen. One path, via the VCPUOP_initialise hypercall, has a bad format character. The BUG() can be hit if VCPUOP_initialise executes for a sufficiently long period of time for a continuation to be created. IMPACT ====== Malicious guests may cause a hypervisor crash, resulting in a Denial of Service (Dos). VULNERABLE SYSTEMS ================== Xen versions 4.6 and newer are vulnerable. Xen versions 4.5 and earlier are not vulnerable. Only x86 PV guests can exploit the vulnerability. HVM and PVH guests, and guests on ARM systems, cannot exploit the vulnerability. MITIGATION ========== There are no mitigations. CREDITS ======= This issue was discovered by Andrew Cooper of Citrix. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa296.patch Xen 4.9 ... unstable xsa296-4.8.patch Xen 4.7 ... 4.8 $ sha256sum xsa296* 71bd433f788dd511fad90165bc5ba9bcabe949eecd912f2a616e3c996960d67d xsa296.meta ccfd81b162b8535d952f56b1f87dfdd960e71bf07c1cf8388976e78e2e86cde5 xsa296.patch b283be3df6789402553172b7fd582bfffb4fa72a6b33543439bd2fb1b87bfbd4 xsa296-4.8.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/4UyVfoK9kFAl2600kMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZn10IAKQhLY9RfkgZhY/6cACYnXqFGWhS6MvyeZrVs1L4 BaojMJilpAo7kc9Xcf+0ThxKI5M/eEeDUdGjFHfBtOUrjOAhaZjaYI1paJwX0JEV QoAMQERTtopFnkCNtvykrMiKZQ2xp6hiios+32PvDdVnjO+rkrKESRNoBVNYlC1f qN8SbZ6m0C5jP4C82ifDEeJHJsVJtfYQSeRl95pgCmsmxxd3x7q7ubPcR6kizT5t Bu4sAtrWNF5zaBrb5kL29yohn4oBLmMV5NO0hSlCbR3FgeFZ7LTwiz8y4d7tVSHg fjbsvhmhfhYO1OnZWFea3QXMgfZjsg6qq9jBnpmGu35WVMY= =xUlU - -----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 iQIVAwUBXbt802aOgq3Tt24GAQgcAxAAgrGOdyKNEEHUZniHUorisqtfchErh/mK O3Q8saal+0QMwL0J8+Jk9G+Ef4l0XsHMzVJScY8mSBCn8jAp/L1D2eJKSrVfLbjY Yrv/iX6S22o94xGZBP9IOsJz5ERCdghjF8EHn0v7dgYYd6hVbqtHG9JiKeURIB8y C9r7ijDcl5jY+/smobYBy4eGrheCGBq8AhvcESf67mt2UAtxlQ4n9fpOsYuyC20p 1pwZZvME4EK5ut0ZG0sx1bzbkzecjlzH8dVxo/V178JC5eOQ/0T7E9Mn+zj6UKUd 2mhhFy8v+y1vLfU70MybPqmIEPhbnflSpxtRp/FLakBJW6S5F3Qei/3ulfUEpObh VigZT6NftoMnnq0vxcXeCcqjiQMdDelcMes5EbI0nm7Kb0Qgkee6wYOxfI3KyKuA 9hmA1ViDIHCnM2ZXDbo9IkHCXu/xXympoDn1Nhv+4njRjpM0f9dIUSHfvKQMsEuG XJb/mQrXzsdCkm6ots6/Z8SiZmBLNxx1FngKsQM+BsQCe1VVBIqt6+oYfLoxR0IT HqVTTB/AIVjZxU6Aqjl6DONfYa2DFUh+1+wEE+H24RDCY04fLKyKRIvNQCDP4TSd TYyKF57ZNsX5WPznWlyBW1ewABSyQmBaJUrF4rlKRRX3RzMvW7YkgDO4+ljNTSdO web7iSBSeMw= =3p06 -----END PGP SIGNATURE-----