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Fri, 20 Jun 2025 17:11:44 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: net@FreeBSD.org Subject: [Bug 287229] IP reassembly issue in FreeBSD 14.1 Date: Fri, 20 Jun 2025 17:11:44 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: 14.2-STABLE X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Some People X-Bugzilla-Who: glebius@FreeBSD.org X-Bugzilla-Status: Open X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: tuexen@freebsd.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="UTF-8" X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated List-Id: Networking and TCP/IP with FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-net List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-net@FreeBSD.org MIME-Version: 1.0 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D287229 --- Comment #31 from Gleb Smirnoff --- On Fri Jun 20 10:03:19 2025 UTC, lucas.aubard@irisa.fr wrote: > We are currently working on Network Intrusion Detection Systems (NIDS) ev= asion > with overlapping IP fragments or TCP segments. > Some NIDSes (Suricata, Snort) propose configuring their IP and TCP reasse= mblies > based on the supervised host OSes as an evasion countermeasure to > overlapping-based attacks. In that context, we test OSes (and other stack= s) to > obtain and describe their reassembly policies so NIDSes can implement and > propose them. > From a NIDS perspective, OS reassembly consistency is thus quite importan= t. Security wise, the coin has two sides. If an attacker can predict what exa= ct fragments would be freed once a system runs out of reassembly queue limits, then they can instrument attacks that would target specific connections. In FreeBSD we salt the hash with a random seed: V_ipq_hashseed =3D arc4random(); This makes distribution of fragment reassemble queue across the hash slots = not predictable by the attacker. For your experiments, you can disable that. = But for the general use of the system, we consider that not a bug, but a featur= e. --=20 You are receiving this mail because: You are on the CC list for the bug.=