CairoSVG vulnerable to Exponential DoS via recursive element amplification

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-31899: 0.52% estimated exploitation activity in the next 30 days; percentile 44.24 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Kozea/CairoSVG (~300K downloads/week) has exponential denial of service via recursive <use element amplification in cairosvg/defs.py (line ~335). This causes CPU exhaustion from a small input. Severity High — CVSS 3.1: 7.5 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Vulnerable Code File: cairosvg/defs.py (line ~335), function use() The use() function recursively processes <use elements without any depth or count limits. With 5 levels of nesting and 10 references each, a 1,411-byte SVG triggers 10^5 = 100,000 render calls. Impact - 1,411-byte SVG payload pins CPU at 100% indefinitely - Memory stays flat at ~43MB — no OOM kill, process never terminates - Any service accepting SVG input (thumbnailing, PDF generation, avatar rendering) is DoS-able - Amplification factor: O(10^N) rendering calls from O(N) input Proof of Concept Save as poc.svg and run timeout 10 cairosvg poc.svg -o test.png: Expected: timeout kills the process after 10 seconds (it never completes on its…

Published by the source

13 Mar 2026, 18:57 UTC

Last modified by the source

13 Jul 2026, 07:26 UTC

Source last checked

26 Oct 2026, 13:40 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-f38f-5xpm-9r7c

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-f38f-5xpm-9r7c

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# Patch Next advisory brief: CVE-2026-31899

Advisory: CairoSVG vulnerable to Exponential DoS via recursive element amplification
IDs: CVE-2026-31899, GHSA-f38f-5xpm-9r7c
Record: https://patchnext.com/advisories/cve-2026-31899 (revision 2, source checked 26 Oct 2026, 13:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: cairosvg 2.9.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI cairosvg: affected <= 2.8.2; fixed in 2.9.0

## Suggested inspection (read-only)
- `python -m pip show cairosvg`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on cairosvg.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-f38f-5xpm-9r7c (OSV record GHSA-f38f-5xpm-9r7c lists affected ranges: PyPI cairosvg >=0 <2.9.0 (fixed))
- Verified: https://github.com/advisories/GHSA-f38f-5xpm-9r7c (GitHub-reviewed advisory GHSA-f38f-5xpm-9r7c lists affected ranges: PyPI cairosvg >=0 <=2.8.2)

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