VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-27932: Moto · joserfc's PBES2 p2c Unbounded Iteration Count enables Denial of Service (DoS)

Affects motoSource GCVE Database

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Authoritative record:CVE-2026-27932· High 7.5

Not known to be exploited · CVSS 7.5 High : upgrade to 5.1.21_2 soon.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 39% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 5.1.21_2

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

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

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: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 3 Mar 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 5.1.21_2.

Affected software

Product	Affected	Fixed in
Homebrewmoto`pkg:brew/moto`Other threats	Affected >=5.0.2 <5.1.21_2	Fixed in 5.1.21_2

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AI-suggested

A patch is available in joserfc version 5.1.21_2 that addresses this vulnerability by bounding the p2c iteration count. Users should upgrade to this fixed version. Additionally, applications should restrict the use of PBES2 algorithms to cases where password-based encryption is necessary and enforce strict algorithm allowlists in JWT/JWE policies. If upgrading immediately is not possible, implementing an upper bound check on the p2c parameter in the decryption function is recommended to prevent excessive iteration counts.

Description

A resource exhaustion vulnerability in the joserfc library allows an unauthenticated attacker to cause a Denial of Service (DoS) by specifying an unbounded iteration count (p2c) in PBES2 password-based encryption during JSON Web Encryption (JWE) token decryption. The p2c parameter controls the number of iterations for the PBKDF2 key derivation function and is not validated or bounded, enabling attackers to force excessive CPU usage. This affects all high-level JWE and JWT decryption interfaces that allow PBES2 algorithms. The vulnerability is fixed in joserfc version 5.1.21_2.

Impact

An unauthenticated remote attacker can cause a Denial of Service by sending crafted JWE/JWT tokens with an excessively large p2c iteration count. This forces the server to perform a computationally expensive key derivation operation, exhausting CPU resources and potentially blocking legitimate users. The attack can occupy server threads or processes for extended periods, proportional to the iteration count specified. There is no impact on confidentiality or integrity, only availability.

Summary

The joserfc library's PBES2 key decryption function reads the p2c (PBES2 Count) iteration parameter directly from the token header without validation. This parameter is used as the iteration count in the PBKDF2 key derivation function. An attacker can specify an extremely large iteration count (e.g., 2^31 - 1), causing the server to consume excessive CPU resources during decryption, resulting in a Denial of Service. The vulnerability affects all JWT policies that permit PBES2 key management algorithms, as the DoS occurs before any claim validation or signature verification. The issue is located in the `decrypt_cek` method of `PBES2HSAlgKeyEncryption` in `jwe_algs.py`. A minimal fix involves bounding the p2c value to a maximum threshold. The vulnerability was confirmed in joserfc version 1.6.2 and is fixed in version 5.1.21_2.

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Affected software

Description

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

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