Read the docs
TI-2026-22276 Aliases CVE-2026-27932GHSA-w5r5-m38g-f9f9

joserfc PBES2 p2c Unbounded Iteration Count enables Denial of Service (DoS)

Priority HIGH 72CWE-770Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-770.

Summary

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. In 1.6.2 and earlier, a resource exhaustion vulnerability in joserfc allows an unauthenticated attacker to cause a Denial of Service (DoS) via CPU exhaustion. When the library decrypts a JSON Web Encryption (JWE) token using Password-Based Encryption (PBES2) algorithms, it reads the p2c (PBES2 Count) parameter directly from the token's protected header. This parameter defines the number of iterations for the PBKDF2 key derivation function. Because joserfc does not validate or bound this value, an attacker can specify an extremely large iteration count (e.g., 2^31 - 1), forcing the server to expend massive CPU resources processing a single token. This vulnerability exists at the JWA layer and impacts all high-level JWE and JWT decryption interfaces if PBES2 algorithms are allowed by the application's policy.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00462 40th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed joserfc (PyPI): 1.6.3

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
authlibjoserfcup to 1.6.2—No fix listedCNA
—joserfc (PyPI)before 1.6.31.6.3Patch availableGHSA-w5r5-m38g-f9f9
  • joserfc Vendorauthlib Affected up to 1.6.2 Fixed in — No fix listed CNA
  • joserfc (PyPI) Vendor— Affected before 1.6.3 Fixed in 1.6.3 Patch available GHSA-w5r5-m38g-f9f9

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:hsiaoming:joserfc:*:*:*:*:*:python:*:*up to 1.6.2VulnerableHsiaoming
  • cpe:2.3:a:hsiaoming:joserfc:*:*:*:*:*:python:*:* Versions up to 1.6.2 Vulnerable ·Hsiaoming

Remediation

  • Fix · GHSA-w5r5-m38g-f9f9 joserfc (PyPI) Fixed in 1.6.3 Advisory →

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product
  • Red Hat

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-27932
  2. 2026-10-03 Alias added: GHSA-w5r5-m38g-f9f9

References

Exploit 1

Patch 1

Advisory 1

Other 2

  • TI-2026-65772 Insufficient verification of data authenticity in Authlib CVSS 3.1CRITICAL 9.8
  • TI-2026-74876 Signature verification bypass in joserfc JWS deserialization CVSS 3.1CRITICAL 9.1
  • TI-2026-22305 Authlib JWS JWK Header Injection: Signature Verification Bypass CVSS 3.1CRITICAL 9.1
  • TI-2025-40202 Resource allocation without limits in authlib joserfc CVSS 4.0CRITICAL 9.2
  • TI-2026-36756 joserfc: HS256/HS384/HS512 verify accepts empty/nil HMAC key (cross-language sibling of CVE-2026-45363) CVSS 4.0HIGH 8.7
  • TI-2026-79518 Authlib fix bypass lets attackers forge HS256 tokens with PEM keys CVSS 3.1CRITICAL 9.1
See all 30 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences