NVD / CVE Program· CNA GitHub_M

CVE-2026-48525: PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS

Noroxi assessment

Priority: Monitor (action score 21/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.37% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: jpadilla pyjwt 2.13.0; azl3 python-jwt 2.8.0-2 on Azure Linux 3.0 2.13.0-1.

Low priority for now. Upgrade to jpadilla pyjwt 2.13.0; azl3 python-jwt 2.8.0-2 on Azure Linux 3.0 2.13.0-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 5.3 · v3.1—No exploit Fix available

Published: May 28, 2026
Updated: Oct 25, 2026
EPSS: 0.3% · 31th percentile
CWE: CWE-400

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 21 / 40 · 5.3 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.3%

CISA SSVC decision

Exploitation: proof of concept
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 5.3; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
pyjwt project	pyjwt	cpe:2.3:a:pyjwt_project:pyjwt

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

pyjwt project pyjwt2.8.0 and later · up to 2.12.1 inclusive

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

jpadilla pyjwt
- >= 2.8.0, < 2.13.0affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	pyjwt	from 0	—
Debian:14	pyjwt	before 2.13.0-1	2.13.0-1
openSUSE:Leap 16.0	python-PyJWT	before 2.12.1-160000.2.1	2.12.1-160000.2.1
openSUSE:Tumbleweed	python-PyJWT	before 2.13.0-1.1	2.13.0-1.1
PyPI	pyjwt	from 2.8.0 · before 2.13.0	2.13.0
SUSE:Linux Enterprise Micro 5.5	python-PyJWT	before 2.4.0-150200.3.14.1	2.4.0-150200.3.14.1
SUSE:Linux Enterprise Module for Public Cloud 15 SP4	python-PyJWT	before 2.8.0-150400.8.13.1	2.8.0-150400.8.13.1
SUSE:Linux Enterprise Server 16.0	python-PyJWT	before 2.12.1-160000.2.1	2.12.1-160000.2.1
SUSE:Linux Micro 6.0	python-PyJWT	before 2.9.0-3.1	2.9.0-3.1
SUSE:Linux Micro 6.1	python-PyJWT	before 2.12.1-slfo.1.1_2.1	2.12.1-slfo.1.1_2.1

Same product

pyjwt project: all records

Other highest-scoring records for the same primary product.

CVE-2026-102268PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion guard
36Monitor
CVE-2026-102267PyJWT: PyJWKClient follows redirects when fetching JWKS
36Monitor
CVE-2026-102266PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation
36Monitor

Published before and after this one in the same product

← EarlierCVE-2026-48523May 28, 2026 · PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys
21Monitor
← EarlierCVE-2026-48524May 28, 2026 · PyJWT: PyJWKClient unbounded JWKS endpoint requests via attacker-controlled kid values (DoS)
14Monitor
Later →CVE-2026-48526May 28, 2026 · PyJWT: Public-key JWK accepted as HMAC secret enables forged HS256 tokens when mixed families are allowed
29Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
jpadilla pyjwt	2.13.0 · description	Vendor (CNA)
azl3 python-jwt 2.8.0-2 on Azure Linux 3.0	2.13.0-1 · CBL-Mariner Releases	Microsoft (MSRC)
debian:pyjwt	2.13.0-1 · Debian:14	Package registry (OSV)
opensuse:python-PyJWT	2.13.0-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
PyPI:pyjwt	2.13.0	Package registry (OSV)
suse:python-PyJWT	2.12.1-slfo.1.1_2.1 · SUSE:Linux Micro 6.1	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: low · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: Low

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

Fix✗ → ✓Sep 28, 2026, 10:46 PM UTC

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