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CVE-2026-48525 medium CVSS 5.3

Vulnerability in pyjwt (CVE-2026-48525)

Summary

Vulnerability in pyjwt (CVE-2026-48525). Risk of unauthorized operations or information disclosure. Exploitable via POST /verify. Mitigation: upgrade to 2.13.0 or later.

Original description

The description as published by the source.

[!NOTE]
Practical impact depends on whether request body-size limits are enforced upstream (proxy/web-server/framework). Deployments with typical body-size caps (≤2 MB) bound the amplifier significantly; deployments accepting larger token inputs are more exposed.

When verifying detached JWS tokens using the unencoded-payload option ("b64": false, RFC 7797), PyJWT performs Base64URL decoding of the compact-serialization payload segment before enforcing the detached-payload rules.

For b64=false, PyJWT later discards that decoded payload and replaces it with the caller-provided detached_payload. In practice, this turns the middle segment into an attacker-controlled “work amplifier”: a remote client can supply an arbitrarily large Base64URL payload segment that forces CPU work + memory allocations even if the signature is invalid.

This creates an unauthenticated DoS vector against any endpoint that verifies detached JWS using PyJWT.

Affected Component(s)

  • jwt/api_jws.py

    • PyJWS.decode() / PyJWS.decode_complete()
    • _load() (parsing and Base64URL decoding)

Root Cause (exact logic flaw)

What happens in the code

In jwt/api_jws.py, decode_complete() does the following (order matters):

  • Calls _load(jwt) first, which decodes the token segments
  • Only after that, checks header.get("b64") and if False, it replaces payload = detached_payload and rebuilds the signing input

This behavior is visible in `decod…

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-2026-48525 has been found in pyjwt.
Attackers can target a specific entry point like POST /verify over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade pyjwt to 2.13.0 or later.
If unsure, ask your IT team or search "pyjwt CVE-2026-48525" on the vendor's site.

CVE-2026-48525 (pyjwt) — CWE-400 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: POST /verify / detached_payload / False / crit
Patched: 2.13.0 — 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 pyjwt. Attackers reach the vulnerable code path via POST /verify without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of pyjwt. Attack surface: POST /verify / detached_payload / False / crit.

🔥 Severity

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

🔧 How to fix

Update to 2.13.0.

🛡️ 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 POST /verify requests with malformed payloads or SQL meta-characters. Run grep -r 'pyjwt' . 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 'pyjwt' . | 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 pyjwt 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
    Hunt for indicators of compromise detect 
    grep 'POST /verify' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで POST /verify への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。

  3. 3
    Apply patch patch 
    Upgrade pyjwt to 2.13.0

    ステージング環境で 2.13.0 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と、Step 2 で見つけた異常検知の続報チェックを含めること。

  4. 4
    Post-deployment verification verify 
    Replay attack against POST /verify on staging to confirm patch closes the vector

    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 Step 2 と同じログクエリでアラート再発が無いか継続監視。

Affected packages

PyPI pyjwt
[{"type":"ECOSYSTEM","events":[{"introduced":"2.8.0"},{"fixed":"2.13.0"}]}]
pip pyjwt
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.13.0"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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