Path Traversal in copier (CVE-2026-53951)
Summary
Path traversal in copier (CVE-2026-53951). Risk of unauthorized operations or information disclosure. Exploitable via trust. Mitigation: upgrade to 9.15.2 or later.
Original description
The description as published by the source.
Copier: trust-prefix bypass via path traversal runs tasks unprompted
Summary
In copier >= 9.5.0, <= 9.15.1, the trust setting's prefix match
(copier/_settings.py) compares the template URL against a trusted prefix with
a raw str.startswith and no path normalization, while the URL is
normalized when the template is actually fetched (Path.resolve() for local
paths; libcurl dot-segment removal for https). A template reference that
textually starts with a trusted prefix but contains ..
(e.g. https://github.com/trusted-org/../attacker-org/repo.git) is therefore
granted trust yet resolves to a different, attacker-controlled template, whose
tasks / migrations / jinja_extensions then run without the --trust
prompt — arbitrary command execution. Likely CWE-22 (Improper Limitation of
a Pathname) in the trust check leading to CWE-94 (code execution).
Details
trust lets users mark template locations as trusted so copier skips the
unsafe-feature gate. A trailing / makes an entry a prefix match
(docs/settings.md: "Locations ending with / will be matched as prefixes,
trusting all templates from that location").
copier/_settings.py:141-146 (tag v9.15.1):
return any(
repository.startswith(_normalize(t))
if t.endswith("/")
else repository == _normalize(t)
for t in trust
)
_normalize only expands ~; it does not touch .. or collapse segments —
`copier/_sett…
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-2026-53951 has been found in copier.
Attackers can target a specific entry point like trust over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade copier to 9.15.2 or later.
If unsure, ask your IT team or search "copier CVE-2026-53951" on the vendor's site.
CVE-2026-53951 (copier) — CWE-22
Attack surface: trust / str.startswith / https / tasks
Patched: 9.15.2 — 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.
Path traversal (CWE-22) exists in copier. Attackers reach the vulnerable code path via trust.
Check the vendor advisory for the affected versions of copier. Attack surface: trust / str.startswith / https / tasks.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 9.15.2.
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 'copier' . 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 'copier' . | 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
copier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 copier to 9.15.2ステージング環境で 9.15.2 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 nvd.nist.gov
- web github.com