# CVE-2026-48525: PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS > Remote attackers can cause denial of service by sending large Base64URL payloads to endpoints verifying detached JWS tokens with specific options. - **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 28 May 2026 - **Updated:** 23 Jun 2026 - **Also known as:** AZL-93042, BELL-CVE-2026-48525, CLEANSTART-2026-CR88221, CLEANSTART-2026-GX50966, DEBIAN-CVE-2026-48525, ECHO-c303-c499-bcc4, GHSA-w7vc-732c-9m39, MINI-264m-qmhh-88rq, MINI-2v39-c68h-33vp, MINI-4fmg-2rg4-4c9v, MINI-4vm5-jqvq-8677, MINI-5c4j-wr54-r2vr, MINI-5f5m-x68q-hcx7, MINI-5j2c-84qv-xhm7, MINI-5rhv-v84q-c8mq, MINI-69jj-989j-549g, MINI-7649-qqxh-fxv7, MINI-7hhj-hw4f-xj7f, MINI-8vgv-46j9-xxgq, MINI-9j84-crrc-rhrh, MINI-9xx5-q7p7-fcpv, MINI-c43r-7q73-8f6p, MINI-cwv4-5rxg-vq6p, MINI-gwfr-9fm2-xx2q, MINI-h8r7-qgmm-58pq, MINI-m4q6-9p75-64cr, MINI-mgx6-q9gm-qg7r, MINI-mh5j-w938-x4vx, MINI-mx95-775h-c7f9, MINI-pr62-g4qf-q65w, MINI-pwhx-mw84-q39f, MINI-qv7g-r4q4-cq75, MINI-qw8f-635m-mgxw, MINI-v59g-97mf-hjr8, MINI-v62h-q6f7-4p28, PYSEC-2026-178, ROOT-APP-PYPI-CVE-2026-48525, UBUNTU-CVE-2026-48525 ## What is CVE-2026-48525? CVE-2026-48525 is a medium-severity denial of service vulnerability in jpadilla pyjwt, published on 28 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description PyJWT is a JSON Web Token implementation in Python. From 2.8.0 to 2.12.1, 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. This vulnerability is fixed in 2.13.0. Weakness: CWE-400 (Uncontrolled Resource Consumption) ## Which versions are affected by CVE-2026-48525? 3 open source packages ship an affected version, including pyjwt. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `pyjwt` | PyPI | From 2.8.0 | 2.13.0 | | `pyjwt` | PyPI | From 2.8.0 | 2.13.0 | | `pyjwt` | PyPI | From 2.8.0 | 2.13.0 | Products: Pyjwt Project Pyjwt. ## How do I fix CVE-2026-48525? Upgrade pyjwt to 2.13.0 or later. ## Is CVE-2026-48525 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48525 exists. ## Other vulnerabilities in jpadilla pyjwt - [CVE-2026-102268](https://insights.sbomify.com/CVE-2026-102268/): PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion guard (critical 9.1) - [CVE-2026-32597](https://insights.sbomify.com/CVE-2026-32597/): PyJWT accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation) (high 7.5) - [CVE-2026-102266](https://insights.sbomify.com/CVE-2026-102266/): PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation (high 7.4) - [CVE-2026-102267](https://insights.sbomify.com/CVE-2026-102267/): PyJWT: PyJWKClient follows redirects when fetching JWKS (high 7.4) - [CVE-2026-102271](https://insights.sbomify.com/CVE-2026-102271/): PyJWT: Public keys in DER form are accepted as HMAC secrets, bypassing the CVE-2022-29217 guard (high 7.4) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-48525 and fix it if it is affected. What it is: CVE-2026-48525 is a medium-severity denial of service vulnerability in jpadilla pyjwt, published on 28 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-48525 exists. Affected packages and fixed versions: - pyjwt (PyPI): affected from 2.8.0; fixed in 2.13.0 - pyjwt (PyPI): affected from 2.8.0; fixed in 2.13.0 - pyjwt (PyPI): affected from 2.8.0; fixed in 2.13.0 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-48525/ (Markdown: https://insights.sbomify.com/CVE-2026-48525/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48525 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48525 - OSV: https://osv.dev/vulnerability/CVE-2026-48525 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-48525/ Summaries are generated and may contain mistakes; the official description above is the record.