CVE-2026-35040VulnerabilityPublished 9 Apr 2026Updated 13 Apr 2026

CVE-2026-35040: nearform fast-jwt · Incorrect Comparison

Affects nearform fast-jwtSource CVE Database V5

Not known to be exploited · CVSS 5.3 Medium : upgrade to 6.2.1 when convenient.

Data as of 25 Oct 2026, 19:02 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 32% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.2.1

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 9 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 2026-10-25.

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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC 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 nearform fast-jwt to 6.2.1.

Affected software

Product	Affected	Fixed in
nearformfast-jwt	Affected <6.2.1	Fixed in 6.2.1
npmfast-jwt`pkg:npm/fast-jwt`Other threats	Affected <6.2.1	Fixed in 6.2.1

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

AI-suggested

Upgrade fast-jwt to version 6.2.1 or later, where this issue is fixed. No other mitigations are indicated or necessary since the vulnerability is resolved in the updated version. Patch status is confirmed by the versioning information in the advisory.

Description

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.1, using certain modifiers on RegExp objects in the allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce options in verify functions can cause certain unintended behaviours. This is because some modifiers are stateful and will cause failures in every second verification attempt regardless of the validity of the token provided. Such modifiers are /g (global matching) and /y (sticky matching). This does NOT allow invalid tokens to be accepted, only for valid tokens to be improperly rejected in some configurations. Instead it causes 50% of valid authentication requests to fail in an alternating pattern. This vulnerability is fixed in 6.2.1.

Impact

The vulnerability causes denial of service for valid authentication requests by rejecting about half of them in an alternating pattern. There is no impact on confidentiality or integrity since invalid tokens are not accepted. The CVSS score is 5.3 (medium severity), reflecting the availability impact without privilege or data compromise.

Summary

The fast-jwt library versions before 6.2.1 have an incorrect comparison issue due to stateful regular expression modifiers used in allowedAud, allowedIss, allowedSub, allowedJti, or allowedNonce options during token verification. Specifically, the global (/g) and sticky (/y) RegExp modifiers cause the verification function to fail every second attempt, leading to valid tokens being rejected intermittently. This behavior does not compromise token acceptance of invalid tokens but impacts availability by causing authentication failures. The vulnerability is tracked as CVE-2026-35040 and is classified under CWE-697 (Incorrect Comparison) and CWE-440 (Expected Behavior Violation).

CWE-697Incorrect Comparison (opens in a new tab)
Pillar weakness
The product compares two entities in a security-relevant context, but the comparison is incorrect.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Attack patterns
Buffer Overflow via Environment Variables (opens in a new tab)
Double Encoding (opens in a new tab)
Client-side Injection-induced Buffer Overflow (opens in a new tab)
Command Delimiters (opens in a new tab)
Flash Injection (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-440Expected Behavior Violation (opens in a new tab)
Base weakness
A feature, API, or function does not perform according to its specification.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 17 Apr 2026, 11:54 UTC

WeaknessesCWE-697, CWE-440

Technical details

References

Community reviews

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