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Message-ID: <CAFdMc-1uX4X1HNrR-hj0iGASCfRL6PfVdNsynOs4BdoS+QrGSw@mail.gmail.com>
Date: Thu, 13 Feb 2025 19:28:29 -0300
From: Daniel Gutson <danielgutson@...il.com>
To: musl@...ts.openwall.com
Cc: oss-security@...ts.openwall.com
Subject: Re: [musl] CVE-2025-26519: musl libc: input-controlled out-of-bounds
write primitive in iconv()
Curious: is there any info about how this was discovered?
El jue, 13 feb 2025, 14:16, Rich Felker <dalias@...c.org> escribió:
> Vulnerability description:
>
> A vulnerability has been identified in musl libc's implementation of
> iconv that can result in out-of-bounds memory writes in applications
> which process untrusted input using iconv and where the input charset
> for the conversion is input-controlled.
>
> In order for the vulnerability to be exposed, an application must call
> iconv_open with an output encoding of UTF-8 and and input encoding of
> EUC-KR, and must subsequently process untrusted input using the
> resulting conversion descriptor. The most common scenario in which
> this occurs is using the declared MIME charset of untrusted input (for
> example, in XML, HTML, or MIME-encoded email) as input to iconv_open
> for converting arbitrary-encoding input to UTF-8.
>
> This issue was discovered and reported by Nick Wellnhofer. It arose as
> a combination of incorrect input byte validation in the EUC-KR
> decoder, and the fact that the UTF-8 output encoder assumed an
> invariant that the input decoder never produces character codes which
> are not valid Unicode Scalar Values.
>
>
>
> Affected versions:
>
> The vulnerable code has been present since EUC-KR support was added to
> iconv in musl 0.9.13. All versions in the range 0.9.13 through 1.2.5
> are affected.
>
> Future releases beginning with 1.2.6 will ship with the bug fixed.
>
>
>
> Mitigation:
>
> All users should apply the source patches included/attached below. The
> first fixes the bug (incorrect input byte validation) responsible for
> the vulnerability, and the second closes off the vector by which this
> class of bug escalated to an out-of-bounds write. These patches should
> apply cleanly to all versions affected by the bug.
>
> Users of musl libc based distributions should obtain an updated
> package with the patch applied through their distributon's update
> channels.
>
> Static-linked binaries that cannot easily be relinked may be patched
> to inhibit the vulnerability, at the cost of disabling support for
> decoding EUC-KR text, by searching the binary, using a
> binary-clean/hex editor, for the byte sequence:
>
> "euckr\0ksc5601\0ksx1001\0cp949\0"
>
> and replacing it with:
>
> "-----\0-------\0-------\0-----\0"
>
> Since non-alphanumeric-ASCII characters are stripped from the charset
> name by iconv_open, this change will render EUC-KR and all aliases for
> it unmatchable, thereby making the vulnerable code unreachable.
>
>
>
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