Vulnerability in WeasyPrint (CVE-2026-106443)
Summary
Vulnerability in WeasyPrint (CVE-2026-106443). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 70.0 or later.
Original description
The description as published by the source.
Summary
This was found during a pentest, funded by the NLNnet foundation, conducted by Stefan Vink from Radically Open Security and the only High issue found.
WeasyPrint passes fetched image bytes directly to Pillow's generic format dispatcher without restricting the input format. When Ghostscript is installed on the host, Pillow's EpsImagePlugin invokes it to rasterize attacker-controlled EPS/PS input. Any content that can supply an image to WeasyPrint (an URL, CSS image value, SVG image reference, or data URI) can therefore drive untrusted PostScript into an external interpreter. On hosts running a Ghostscript version with a known -dSAFER bypass, this yields remote code execution.
Details
The image pipeline reads an external response and hands the raw bytes to Pillow's format-agnostic Image.open, with no allowlist of safe raster formats:
with fetch(url_fetcher, url) as response:
bytestring = response.read()
mime_type = forced_mime_type or response.content_type
...
pillow_image = Image.open(BytesIO(bytestring))
Pillow selects the handler from the byte signature. For EPS/PS input it selects PIL.EpsImagePlugin, which invokes Ghostscript to rasterize the input when a Ghostscript executable is available. Modern Ghostscript builds may run with -dSAFER, but that does not remove the interpreter boundary — it only constrains it, and multiple CVEs have bypassed it.
The defect in WeasyPrint is that it dispatches untrusted bytes to a format handler capable of…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-106443 has been found in WeasyPrint.
Successful exploitation can lead to full system takeover. CVSS score: 8.8/10.
What to do: upgrade WeasyPrint to 70.0 or later.
If unsure, ask your IT team or search "WeasyPrint CVE-2026-106443" on the vendor's site.
CVE-2026-106443 (WeasyPrint) — CWE-20 / CVSS v3 8.8
Attack vector: remote (network-reachable) / no user interaction
Patched: 70.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-20) exists in WeasyPrint.
Check the vendor advisory for the affected versions of WeasyPrint.
Severity: High (CVSS 8.8/10). Successful exploitation can lead to full system takeover.
Update to 70.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'WeasyPrint' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'WeasyPrint' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
WeasyPrintを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade WeasyPrint to 70.0ステージング環境で 70.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- web github.com
- web github.com
- web github.com
- web nvd.nist.gov
- web github.com