VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-49852: joserfc · HS256/HS384/HS512 verify accepts empty/nil HMAC key (cross-language sibling of CVE-2026-45363)

Affects motoSource GCVE Database

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Mentioned vulnerabilities

CVE-2026-45363

Not known to be exploited · CVSS 8.7 High : upgrade to 5.2.2 soon.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 4.0 base score

8.7High

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

EPSS: 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 5.2.2

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: High
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 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 29 Oct 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 moto to 5.2.2.

Affected software

Product	Affected	Fixed in
Homebrewmoto`pkg:brew/moto`Other threats	Affected >=5.0.2 <5.2.2	Fixed in 5.2.2

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

AI-suggested

A patch is available in joserfc version 5.2.2 that fixes this issue. Users should upgrade to version 5.2.2 or later to mitigate this vulnerability. Until patched, ensure that JWT secret keys are never empty or None by validating configuration sources and environment variables. Avoid defaulting to empty strings for secrets and implement application-level checks to reject empty keys before calling joserfc.jwt.decode.

Description

The joserfc library's JWT decoding function accepts attacker-forged HMAC-signed tokens when the verification key is empty or None. This occurs because the library does not reject zero-length HMAC keys, allowing attackers to forge tokens without secret knowledge if the configured secret is empty. This vulnerability affects joserfc versions up to 1.6.7 with no patched release available at the time of this report.

Impact

An attacker can forge valid HMAC-signed JWT tokens without knowledge of the secret key if the verification key is empty or None. This can lead to unauthorized access or privilege escalation in applications relying on joserfc for JWT verification. The vulnerability requires no authentication and can be exploited remotely if the application uses joserfc.jwt.decode with a misconfigured or empty secret key.

Summary

The joserfc library's HMACAlgorithm class uses Python's hmac.new function for signing and verification but does not reject empty or nil HMAC keys. The import_key method only warns if the key length is less than 14 bytes but does not reject zero-length keys, allowing an empty key to be used in verification. This flaw enables attackers to forge JWT tokens if the verification key is empty or None, a condition that can arise from misconfiguration such as unset environment variables or missing database entries. This vulnerability is a cross-language sibling of CVE-2026-45363 affecting ruby-jwt, which was fixed by rejecting empty keys. No fixed release for joserfc is available yet.

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Description

AI analysisMachine-generated, updated 30 Oct 2026, 05:44 UTC

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