Vulnerability in pyjwt (CVE-2026-48523)
Summary
Vulnerability in pyjwt (CVE-2026-48523). Risk of unauthorized operations or information disclosure. Exploitable via PyJWK. Mitigation: upgrade to 2.13.0 or later.
Original description
The description as published by the source.
[!NOTE]
Scored assuming a deployment where algorithm policy functions as an authentication/authorization boundary. In deployments where the algorithm policy enforces crypto agility only, the practical confidentiality impact is lower and the issue is closer to an integrity-of-policy-enforcement bug.
PyJWT 2.9.0 through 2.12.1 allows a verifier-side algorithm allow-list bypass when jwt.decode() or jwt.decode_complete() are called with a PyJWK key. The token header alg is checked against the caller-supplied algorithms allow-list, but signature verification is performed with the algorithm bound to the PyJWK object instead of the header algorithm. An attacker who controls a registered JWK/JWKS private key can sign with a disallowed algorithm, advertise an allowed algorithm in the JWT header, and still be accepted. The issue affects the documented PyJWKClient.get_signing_key_from_jwt(...) flow.
Summary
PyJWT's PyJWK verification path allows a verifier-side algorithm allow-list bypass.
In affected versions, when a JWT is decoded with a PyJWK object, PyJWT verifies that the header alg string is present in the caller's algorithms=[...] list, but it does not actually use the header algorithm to verify the signature. Instead, it verifies with the algorithm already bound to the PyJWK object.
This lets an attacker who controls a registered JWK/JWKS private key sign with a disallowed algorithm and have the token accepted as long as the JWT header ad…
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-2026-48523 has been found in pyjwt.
Attackers can target a specific entry point like PyJWK over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.4/10.
What to do: upgrade pyjwt to 2.13.0 or later.
If unsure, ask your IT team or search "pyjwt CVE-2026-48523" on the vendor's site.
CVE-2026-48523 (pyjwt) — CWE-347 / CVSS v3 5.4
Attack vector: remote (network-reachable) / no user interaction
Attack surface: PyJWK / alg / algorithms / PyJWKClient
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.
A vulnerability (CWE-347) exists in pyjwt. Attackers reach the vulnerable code path via PyJWK.
Check the vendor advisory for the affected versions of pyjwt. Attack surface: PyJWK / alg / algorithms / PyJWKClient.
Severity: Medium (CVSS 5.4/10). Risk of unauthorized operations or information disclosure.
Update to 2.13.0.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. 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
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1Identify 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。 -
2Apply 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を含めること。
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3Post-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
Fix status by distribution
Fixed packages published by each distribution for this CVE
- BellSoft Alpaquita BELL-CVE-2026-48523 py3-jwt Fixed in: 2.13.0-r0
- Debian DEBIAN-CVE-2026-48523 pyjwt
- Ubuntu UBUNTU-CVE-2026-48523 pyjwt
References
- advisory nvd.nist.gov
- exploit github.com
- package github.com
- web github.com
- web github.com