VulnerabilityPublished 28 Sep 2026Updated 1 Oct 2026

CVE-2026-102265: jpadilla pyjwt · Uncontrolled Recursion

Affects jpadilla pyjwtSource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium : upgrade to 2.14.0 when convenient.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 28% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 2.14.0

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade jpadilla pyjwt to 2.14.0.

Affected software

Product	Affected	Fixed in
jpadillapyjwt	Affected >=2.13.0 <2.14.0	Fixed in 2.14.0
PyPIpyjwt`pkg:pypi/pyjwt`Other threats	Affected >=2.13.0 <2.14.0	Fixed in 2.14.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade PyJWT to version 2.14.0 or later, which includes a fix that catches RecursionError during JWT header parsing and raises DecodeError instead. This prevents unhandled exceptions and ensures malformed tokens are safely rejected. Until upgrading, consider implementing additional input validation or limiting token size and nesting depth at the application level. No other actions are required as the fix is officially released.

Description

PyJWT versions from 2.13.0 up to but not including 2.14.0 contain a vulnerability where deeply nested JSON arrays in the JWT header cause a RecursionError during parsing. This error is not caught by the library's usual exception handling, resulting in an HTTP 500 server error and a full traceback logged. This allows unauthenticated attackers to cause a denial of service on JWT validation endpoints without crashing the server or exposing data. The issue is fixed in PyJWT 2.14.0.

Impact

An unauthenticated attacker can send a crafted JWT token with a deeply nested JSON header to cause a denial of service by triggering a RecursionError during token parsing. This results in HTTP 500 errors instead of expected 401 Unauthorized responses and logs full tracebacks. The service remains alive but the authentication path is disrupted, allowing repeated cheap and deterministic denial of service attacks without requiring valid keys or signatures. No data exposure or crash occurs.

Summary

PyJWT's _load() method parses the JWT header JSON and catches ValueError exceptions to raise DecodeError, ensuring untrusted input is handled safely. However, deeply nested JSON arrays exceeding the Python recursion limit trigger a RecursionError, which is not caught and escapes the PyJWTError exception handling. This leads to an unhandled exception causing HTTP 500 errors and tracebacks in logs on endpoints validating JWT tokens. The vulnerability affects versions >=2.13.0 and <2.14.0. The fix, committed and released in PyJWT 2.14.0, adds handling for RecursionError by translating it into DecodeError, restoring safe error handling for malformed tokens.

CWE-674Uncontrolled Recursion (opens in a new tab)
Class weakness
The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack.
Implementation
Ensure that an end condition will be reached under all logic conditions. The end condition may include checking against the depth of recursion and exiting with an error if the recursion goes too deep. The complexity of the end condition contributes to the effectiveness of this action.
Implementation
Increase the stack size.
Attack patterns
Serialized Data with Nested Payloads (opens in a new tab)
Oversized Serialized Data Payloads (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 17 Oct 2026, 22:48 UTC

WeaknessesCWE-674

Technical details

References

Community reviews

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