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Date: Mon, 25 Sep 2023 12:29:11 +0200
From: Solar Designer <>
Subject: CVE-2023-4527: glibc: Stack read overflow in getaddrinfo in no-aaaa mode


A bug affecting glibc 2.36+ was reported and fixed earlier this month:

> 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 <>
> Date:   Fri Jun 24 18:16:41 2022 +0200
>     resolv: Implement no-aaaa stub resolver option
>     Reviewed-by: Carlos O'Donell <>

> 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:

> 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:

The feature is described in a glibc NEWS entry for 2.36 as follows:

> * 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.


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