Vulnerability in league/flysystem (CVE-2026-102601)
Summary
Vulnerability in league/flysystem (CVE-2026-102601). Risk of unauthorized operations or information disclosure. Exploitable via false. Mitigation: upgrade to 3.35.3 or later.
Original description
The description as published by the source.
Related public issue (context, not a duplicate)
Closed issue #1429 ("Handle non-UTF-8 paths", 2024-03-24) raised exactly this general concern and
even suggested detection via preg_match('//u', $path) !== 1 -- note the reporter's suggested check
explicitly compares !== 1, which would correctly treat PCRE's false return as "reject." The
maintainer's reply pointed to the PathNormalizer interface as the place to implement this. The
control-character check that ended up shipping in WhitespacePathNormalizer
(if (preg_match('#\p{C}+#u', $unixPath))) addresses the general concern but does not use the
!== 1-style comparison the original issue suggested -- it uses a bare truthy check, which is exactly
the gap this report demonstrates. So this is not a duplicate of #1429; it's a concrete bypass
surviving in the fix that issue's concern led to.
Vulnerability Details
File: src/WhitespacePathNormalizer.php, lines 22-28 (normalizePath()) -- the default
PathNormalizer used by Filesystem for every adapter (Local, FTP, SFTP, S3, AsyncAwsS3, Azure, GCS,
ZipArchive, GridFS, InMemory) unless the application supplies a custom one.
Root Cause
public function normalizePath(string $path): string
{
$unixPath = str_replace('\\', '/', $path);
if (preg_match('#\p{C}+#u', $unixPath)) {
throw CorruptedPathDetected::forPath($path);
}
...
preg_match() returns false (a PHP engine error) rather than 0 when the subject…
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-2026-102601 has been found in league/flysystem.
Attackers can target a specific entry point like false over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 3.5/10.
What to do: upgrade league/flysystem to 3.35.3 or later.
If unsure, ask your IT team or search "league/flysystem CVE-2026-102601" on the vendor's site.
CVE-2026-102601 (league/flysystem) — CWE-150 / CVSS v3 3.5
Attack vector: remote (network-reachable)
Attack surface: false / PathNormalizer / WhitespacePathNormalizer / Filesystem
Patched: 3.35.3 — 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-150) exists in league/flysystem. Attackers reach the vulnerable code path via false.
Check the vendor advisory for the affected versions of league/flysystem. Attack surface: false / PathNormalizer / WhitespacePathNormalizer / Filesystem.
Severity: Low (CVSS 3.5/10). Risk of unauthorized operations or information disclosure.
Update to 3.35.3.
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 'league/flysystem' . 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 'league/flysystem' . | 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
league/flysystem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 league/flysystem to 3.35.3ステージング環境で 3.35.3 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
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com