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Out-of-bounds ReadWeakness · CWE-125

CVE-2025-15646

CRITICAL · 9.8 CVSS v3.1 Published 2026-07-01
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click Patch available 8 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
HTML::Gumbo versions before 0.19 for Perl disclose heap memory via type confusion. Support for the <template> element was added to libgumbo 0.10.0 in 2015, but the walk_tree function in lib/HTML/Gumbo.xs was not updated to support it. The element was treated as a text-node, where strlen() over-reads the heap block that the pointer addresses. Any caller that runs parse() with the default format => 'string', or with format => 'tree', on input containing a <template> element serializes the over-read bytes into the returned result, disclosing bounded heap contents. format => 'callback' reaches a croak on the unhandled node type and is unaffected.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

HTML::Gumbo versions before 0.19 for Perl suffer from a heap memory disclosure vulnerability due to improper handling of the <template> element. The walk_tree function in the C XS layer was not updated when libgumbo 0.10.0 added <template> element support in 2015, causing the element to be treated as a text-node where strlen() over-reads the heap block. When parse() is called with format => 'string' or format => 'tree' on input containing <template> elements, the over-read heap contents are serialized into the returned result.

MitigationUpgrade to HTML::Gumbo version 0.19 or later, which includes the fix for proper <template> element handling in the walk_tree function. Until then, avoid parsing untrusted HTML containing <template> elements or use format => 'callback' as a workaround.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed HTML::Gumbo version
    Run: perl -MHTML::Gumbo -e 'print $HTML::Gumbo::VERSION' or check via cpanm/cpan listing
    Affected if Version is below 0.19 (e.g., 0.18, 0.17, etc.)
  2. Identify parse() calls using vulnerable formats
    Search Perl codebase for HTML::Gumbo->parse calls with format => 'string' or format => 'tree' arguments
    Affected if Code uses format => 'string' or format => 'tree' (not format => 'callback')
  3. Determine if untrusted HTML with template elements is processed
    Review HTML input sources parsed by HTML::Gumbo and check if they could contain <template> tags from user-controlled sources
    Affected if Input may contain <template> elements from untrusted sources
  4. Verify heap disclosure risk via output inspection
    Parse a test document containing <template> elements and examine output for unexpected binary data or memory contents
    Affected if Output contains unexpected data beyond the expected serialized HTML structure

You are affected if HTML::Gumbo version is below 0.19 AND you parse HTML containing <template> elements using format => 'string' or format => 'tree'.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch github.com →
Interim mitigation

Upgrade to HTML::Gumbo version 0.19 or later, which includes the fix for proper <template> element handling in the walk_tree function. Until then, avoid parsing untrusted HTML containing <template> elements or use format => 'callback' as a workaround.

Recommended fix High confidence

HTML::Gumbo version 0.19

  1. Check current version of HTML::Gumbo installed: perl -MHTML::Gumbo -e 'print $HTML::Gumbo::VERSION'
  2. Upgrade to version 0.19 or later using cpan or cpanm: cpan HTML::Gumbo or cpanm HTML::Gumbo
  3. Verify the upgrade was successful by checking the new version matches 0.19 or higher

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,780
Get the patch applied

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,848.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-15646 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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