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Message-ID: <20230925102911.GA4097@openwall.com>
Date: Mon, 25 Sep 2023 12:29:11 +0200
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Subject: CVE-2023-4527: glibc: Stack read overflow in getaddrinfo in no-aaaa mode
Hi,
A bug affecting glibc 2.36+ was reported and fixed earlier this month:
https://sourceware.org/bugzilla/show_bug.cgi?id=30842
> Florian Weimer 2023-09-12 15:16:27 UTC
>
> If the system is configured in no-aaaa mode via /etc/resolv.conf,
> getaddrinfo is called for the AF_UNSPEC address family, and a DNS
> response is received over TCP that is larger than 2048 bytes,
> getaddrinfo may potentially disclose stack contents via the returned
> address data, or crash. While name lookup normally just fails
> incorrectly, crashes are not difficult to trigger, with valid DNS
> responses that are propagated by DNS resolvers.
>
> Introduced by:
>
> commit f282cdbe7f436c75864e5640a409a10485e9abb2
> Author: Florian Weimer <fweimer@...hat.com>
> Date: Fri Jun 24 18:16:41 2022 +0200
>
> resolv: Implement no-aaaa stub resolver option
>
> Reviewed-by: Carlos O'Donell <carlos@...hat.com>
> Florian Weimer 2023-09-13 12:58:01 UTC
>
> All impacted branches fixed.
Even though upstream 2.35 and older are not affected, the problematic
commit was backported into some distro packages of older glibc:
https://access.redhat.com/security/cve/CVE-2023-4527
> Statement
> This issue only affect systems configured with no-aaaa mode via
> /etc/resolv.conf.
>
> The no-aaaa stub resolver option was backported only to Red Hat
> Enterprise Linux versions 8.7 and 9.1. Therefore, previous versions are
> not affected.
>
> Mitigation
> Removing the no-aaaa diagnostic option from /etc/resolv.conf will
> mitigate this flaw.
Also tracked here:
https://bugzilla.redhat.com/show_bug.cgi?id=2234712
The feature is described in a glibc NEWS entry for 2.36 as follows:
https://lists.gnu.org/archive/html/info-gnu/2022-08/msg00000.html
> * The "no-aaaa" DNS stub resolver option has been added. System
> administrators can use it to suppress AAAA queries made by the stub
> resolver, including AAAA lookups triggered by NSS-based interfaces
> such as getaddrinfo. Only DNS lookups are affected: IPv6 data in
> /etc/hosts is still used, getaddrinfo with AI_PASSIVE will still
> produce IPv6 addresses, and configured IPv6 name servers are still
> used. To produce correct Name Error (NXDOMAIN) results, AAAA queries
> are translated to A queries. The new resolver option is intended
> primarily for diagnostic purposes, to rule out that AAAA DNS queries
> have adverse impact. It is incompatible with EDNS0 usage and DNSSEC
> validation by applications.
Alexander
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