Bug#1144490: libxapian30: previously missed corner case of CVE-2018-0499

Package: libxapian30
Version: 1.4.31-2
Fixed: 1.4.32-1
Severity: serious
Tags: security
Justification: potential security vulnerability
X-Debbugs-Cc: Debian Security Team <[email protected]>

This was reported to upstream's public development list:

https://lists.xapian.org/pipermail/xapian-devel/2026-August/003429.html

The bug is missing HTML escaping, potentially allowing an attacker to inject
unescaped data into generated HTML search results.  It's effectively a
corner case missed when we fixed CVE-2018-0499.

It affects upstream releases 1.4.x for x <= 31 and 2.0.0.
Upstream releases 1.4.32 and 2.0.1 include a fix, and I've already
uploaded 1.4.32 to unstable and 2.0.1 to experimental.

There are patches here:

https://trac.xapian.org/wiki/SecurityFixes/2018-07-02#a2026-08-13update
The actually fix is just this (the patches also add test coverage):


     if (hi_start.empty() && hi_end.empty() && text.size() <= length) {        
-        // Too easy!
-        return text;
+        // The text is already short enough so we just need to perform
+        // escaping.
+        string output;
+        append_escaping_xml(text.data(), text.data() + text.size(), output);
+        return output;
     }

The 4 variables in the condition are all parameters from the
MSet::snippet() API call.  In order to be exploited, hi_start and hi_end
need to be passed as empty strings (they have default values which
aren't empty).  I'd expect most usage in a web context would want to
highlight matching terms in the snippet and so it's probably uncommon to
pass empty string here - I looked for an example of such usage with
codesearch.d.n but didn't find anything.

However empty highlighting strings are a legitimate way to call this
method, and I may have missed an instance, or such use may be present in
code that hasn't been packaged for Debian.  Therefore I think we should
apply this patch to stable.

I've already contacted the security team and they said we should handle
this via a stable update.

Cheers,
    Olly