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Message-ID: <20260123181143.GT1827@brightrain.aerifal.cx>
Date: Fri, 23 Jan 2026 13:11:43 -0500
From: Rich Felker <dalias@...c.org>
To: Richard Howe <rhowe425@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: denial-of-service issue in musl’s iconv implementation
On Fri, Jan 23, 2026 at 10:17:51AM -0500, Richard Howe wrote:
> Hello,
>
> I am reporting a denial-of-service issue in musl’s iconv implementation.
> Summary
>
> A crafted input passed to iconv() can trigger an internal assertion failure
> in gconv():
>
> ../iconv/skeleton.c:745: gconv: Assertion `outbuf == outerr' failed
>
> This causes the process to abort, resulting in a denial of service.
> Affected versions
>
> Tested on musl 1.2.5 (x86_64).
> I have not tested earlier versions.
> Impact
>
> This issue allows untrusted input to reliably crash processes using iconv().
> The failure occurs via an internal invariant violation and results in
> abort().
>
> When musl is rebuilt with assertions disabled (-DNDEBUG), the same input no
> longer crashes and does not appear to cause memory corruption, indicating
> this is a DoS issue rather than an RCE.
> Reproduction
>
> The issue is reproducible using a simple harness that invokes iconv_open()
> and iconv() on attacker‑controlled input.
>
> Steps:
>
> 1.
>
> Build musl normally (assertions enabled).
> 2.
>
> Compile the attached harness against musl.
> 3.
>
> Run the harness with the provided input file.
>
> The process aborts with the assertion above.
>
> I am happy to provide:
>
> -
>
> the minimal crashing input
> -
>
> the reproduction harness
> -
>
> additional debugging information if needed
>
> Thank you for your time.
>
> Best regards,
> Richard Howe
>
>
> [image: image.png]
The attached png is clearly showing a backtrace of a glibc-linked
program not a musl-linked one. Can you please clarify.
Rich
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