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CVE-2026-49852

Authentication Bypass in joserfc (CVE-2026-49852)

Summary

Authentication bypass in joserfc (CVE-2026-49852). Risk of unauthorized operations or information disclosure. Exploitable via joserfc.jwt.decode. Mitigation: upgrade to 1.6.8 or later.

Original description

The description as published by the source.

Summary

joserfc.jwt.decode accepts attacker-forged HMAC-signed tokens when the
caller-supplied verification key is the empty string or None.
HMACAlgorithm.sign and HMACAlgorithm.verify in
src/joserfc/_rfc7518/jws_algs.py:62-70 feed whatever
OctKey.get_op_key(...) produced into hmac.new(...), and OctKey.import_key
only emits a SecurityWarning when the raw key is shorter than 14 bytes
without rejecting zero-length input. Any application whose JWT secret is
sourced from an unset environment variable, an unset Redis / DB row, a key
finder fallback that returns "", or a Hash.new("")-style default verifies
attacker tokens forged with HMAC(key=b"", signing_input) because the
attacker trivially reproduces the same digest with no secret knowledge.

This is a cross-language sibling of jwt/ruby-jwt GHSA-c32j-vqhx-rx3x /
CVE-2026-45363 (HS256/HS384/HS512 verify accepted an empty/nil HMAC key,
filed 2026-05-13). ruby-jwt v3.2.0 added an ensure_valid_key! precondition
that rejects empty keys at both sign and verify entry; joserfc has no
equivalent. (The same primitive lives in the deprecated authlib.jose
module by the same maintainer; filing this advisory against joserfc
alongside a separate authlib advisory because the codebases are
independent shipping artifacts on PyPI.)

Affected versions

joserfc (PyPI) <= 1.6.7 (latest…

Source: GitHub Security Advisories (Global) 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-2026-49852 has been found in joserfc.
Attackers can target a specific entry point like joserfc.jwt.decode over the network to misuse the product.
Risk of unauthorized operations or information disclosure.
What to do: upgrade joserfc to 1.6.8 or later.
If unsure, ask your IT team or search "joserfc CVE-2026-49852" on the vendor's site.

CVE-2026-49852 (joserfc) — CWE-287
Attack surface: joserfc.jwt.decode / None / HMACAlgorithm.sign / HMACAlgorithm.verify
Patched: 1.6.8 — 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

Authentication bypass (CWE-287) exists in joserfc. Attackers reach the vulnerable code path via joserfc.jwt.decode.

📍 Affected scope

Check the vendor advisory for the affected versions of joserfc. Attack surface: joserfc.jwt.decode / None / HMACAlgorithm.sign / HMACAlgorithm.verify.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 1.6.8.

🛡️ 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 'joserfc' . 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 'joserfc' . | 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 joserfc 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 joserfc to 1.6.8

    ステージング環境で 1.6.8 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

pip joserfc
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.6.8"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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