Re: [SECURITY] [DSA 4272-1] linux security update
Hi, On Wed, Aug 15, 2018 at 04:02:59PM +0200, Matus UHLAR - fantomas wrote: > Hello, > > On 14.08.18 21:52, Salvatore Bonaccorso wrote: > > CVE-2018-5391 (FragmentSmack) > > > >Juha-Matti Tilli discovered a flaw in the way the Linux kernel > >handled reassembly of fragmented IPv4 and IPv6 packets. A remote > >attacker can take advantage of this flaw to trigger time and > >calculation expensive fragment reassembly algorithms by sending > >specially crafted packets, leading to remote denial of service. > > > >This is mitigated by reducing the default limits on memory usage > >for incomplete fragmented packets. The same mitigation can be > >achieved without the need to reboot, by setting the sysctls: > > > >net.ipv4.ipfrag_high_thresh = 262144 > >net.ipv6.ip6frag_high_thresh = 262144 > >net.ipv4.ipfrag_low_thresh = 196608 > >net.ipv6.ip6frag_low_thresh = 196608 > > It seems that the thresholds should be applied in reverse order, the stretch > kernel complains if we try to shring the high threshold below the low one > (and is probably right). Yes that's right. I have fixed this information/listing in the webversion of the DSA, but cannot be fixed for the sent mail. I asked debian-www team if the listing can be improved there. Regards, Salvatore
Re: [SECURITY] [DSA 4272-1] linux security update
Hello, On 14.08.18 21:52, Salvatore Bonaccorso wrote: CVE-2018-5391 (FragmentSmack) Juha-Matti Tilli discovered a flaw in the way the Linux kernel handled reassembly of fragmented IPv4 and IPv6 packets. A remote attacker can take advantage of this flaw to trigger time and calculation expensive fragment reassembly algorithms by sending specially crafted packets, leading to remote denial of service. This is mitigated by reducing the default limits on memory usage for incomplete fragmented packets. The same mitigation can be achieved without the need to reboot, by setting the sysctls: net.ipv4.ipfrag_high_thresh = 262144 net.ipv6.ip6frag_high_thresh = 262144 net.ipv4.ipfrag_low_thresh = 196608 net.ipv6.ip6frag_low_thresh = 196608 It seems that the thresholds should be applied in reverse order, the stretch kernel complains if we try to shring the high threshold below the low one (and is probably right). For the stable distribution (stretch), this problem has been fixed in version 4.9.110-3+deb9u2. (just a note for those who can't just reboot). -- Matus UHLAR - fantomas, uh...@fantomas.sk ; http://www.fantomas.sk/ Warning: I wish NOT to receive e-mail advertising to this address. Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu. The 3 biggets disasters: Hiroshima 45, Tschernobyl 86, Windows 95
[SECURITY] [DSA 4272-1] linux security update
-BEGIN PGP SIGNED MESSAGE- Hash: SHA512 - - Debian Security Advisory DSA-4272-1 secur...@debian.org https://www.debian.org/security/ Salvatore Bonaccorso August 14, 2018 https://www.debian.org/security/faq - - Package: linux CVE ID : CVE-2018-5391 CVE-2018-5391 (FragmentSmack) Juha-Matti Tilli discovered a flaw in the way the Linux kernel handled reassembly of fragmented IPv4 and IPv6 packets. A remote attacker can take advantage of this flaw to trigger time and calculation expensive fragment reassembly algorithms by sending specially crafted packets, leading to remote denial of service. This is mitigated by reducing the default limits on memory usage for incomplete fragmented packets. The same mitigation can be achieved without the need to reboot, by setting the sysctls: net.ipv4.ipfrag_high_thresh = 262144 net.ipv6.ip6frag_high_thresh = 262144 net.ipv4.ipfrag_low_thresh = 196608 net.ipv6.ip6frag_low_thresh = 196608 The default values may still be increased by local configuration if necessary. For the stable distribution (stretch), this problem has been fixed in version 4.9.110-3+deb9u2. We recommend that you upgrade your linux packages. For the detailed security status of linux please refer to its security tracker page at: https://security-tracker.debian.org/tracker/linux Further information about Debian Security Advisories, how to apply these updates to your system and frequently asked questions can be found at: https://www.debian.org/security/ Mailing list: debian-security-announce@lists.debian.org -BEGIN PGP SIGNATURE- iQKTBAEBCgB9FiEERkRAmAjBceBVMd3uBUy48xNDz0QFAltzSylfFIAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldDQ2 NDQ0MDk4MDhDMTcxRTA1NTMxRERFRTA1NENCOEYzMTM0M0NGNDQACgkQBUy48xND z0RaQQ//ZmbZqbqzS25ZDtEN7fJbInoznmfFiXHYCS9/GNEID3ODvPEn34omQ+Tj HJHroMWFsXROIaViHvJ2mZB3dpgv+ge1huvqXFTh+VrnQxvmdzzNy0UiDUH3B7jU BnbI7IS5x2dBC4cY+5vJ1fn0mWnvh/Bg9D+HEce3mmz9f/bTmXXiwPosyCM0KnzC R8aq73EU61A+IYJd+otICU6jZk+4IdgZRhW6q8F5OgHrnBryr0Xem8hSeL4Nkv3y aLX2Ca20eAgfeGo/SAHmG+FfJLR6dG8frz1k8HsKWNW16O8AC6lDbRC1+teK1e43 6GoIjfU9fBy3Cc35I1JQ85cfzfDLaETQ6IQ23o9SUP6qh8QKtUYDIU2sEDAThmrA IeoJsscGUvRMOx/XzuW8xN6rgbU+uNp8NIYXonZjy+U28dGp11obq3ka02railwj VEhm3YPIddeySofS0tZuBJ1XKL1/a5voLQ9GEBk+wq10DPdfYvSmIXxVR/FOfYy5 mLLTdtHINomfeihEI9AOWqq7w5bVIIidWB2a5FJiBZKWW1OdiNRHlD4hNMCR5xRv vK2PPXYcCxBuO4mdcnYydDcmrDvD22b6AhN1sm8FqUkWSXQbRoHNan95A8KbgZw0 Rk68oRCEFKcScB67ZhK2hUue7hZhkz52MlbS7pJgBPSuKrVsZtw= =WPm5 -END PGP SIGNATURE-
