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CVE-2026-102277 medium CVSS 5.3

Vulnerability in brace-expansion (CVE-2026-102277)

Summary

Vulnerability in brace-expansion (CVE-2026-102277). Risk of unauthorized operations or information disclosure. Exploitable via escClose. Mitigation: upgrade to 1.1.21 or later.

Original description

The description as published by the source.

Summary

Expanding {a},b}-shaped input takes time quadratic in the number of literal } characters, blocking the event loop.

Bash preserves a quirk where a brace group followed by a comma set still expands ({a},b}). The parser implements this by rewriting the string and restarting the scan. Each pass absorbs exactly one } and re-scans from the beginning, so n trailing braces cost n full passes.

Reproduction

const build = n => '{a}' + '}'.repeat(n) + ',z}'

for (const n of [8000, 16000, 32000, 64000, 128000]) {
  const t = Date.now()
  expand(build(n))
  console.log(n, Date.now() - t + 'ms')
}
n input time results
8,000 8 KB 110 ms 2
16,000 16 KB 446 ms 2
32,000 32 KB 1.7 s 2
64,000 64 KB 6.9 s 2
128,000 128 KB 27.7 s 2

ms/n^2 is flat at ~1.7 and each doubling of n costs exactly 4.0x - quadratic. 128 KB of input blocks the event loop for nearly half a minute to produce two results.

Mechanism

Instrumenting the rewrite branch confirms it runs exactly n + 1 times, once per literal }, each re-scanning the whole string.

There is a second multiplier. The rewrite replaces the group's closing } with the internal escClose sentinel, which is '\0CLOSE' + Math.random() + '\0' - about 25 characters. The working string therefore grows by ~25 characters on every pass:

n input length final string length
1,000 1,006 26,006
8…

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-2026-102277 has been found in brace-expansion.
Attackers can target a specific entry point like escClose over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade brace-expansion to 1.1.21 or later.
If unsure, ask your IT team or search "brace-expansion CVE-2026-102277" on the vendor's site.

CVE-2026-102277 (brace-expansion) — CWE-400 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: escClose / max / maxLength / minimatch
Patched: 1.1.21 — 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.

❓ What is the problem

A vulnerability (CWE-400) exists in brace-expansion. Attackers reach the vulnerable code path via escClose without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of brace-expansion. Attack surface: escClose / max / maxLength / minimatch.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.1.21.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'brace-expansion' . 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

  1. 1
    Identify exposure identify 
    grep -r 'brace-expansion' . | 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 brace-expansion を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade brace-expansion to 1.1.21

    ステージング環境で 1.1.21 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。

  3. 3
    Post-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

npm brace-expansion
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.1.21"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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