VulnerabilityPublished 31 Oct 2026

CVE-2026-119284: joserfc · Compact JWS size guard allocates attacker-controlled segments before rejection

Affects kimi-cliSource GCVE Database

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Authoritative record:CVE-2026-119284· Medium 6.9

Not known to be exploited · CVSS 6.9 Medium.

Data as of 31 Oct 2026, 15:55 UTC

CVSS 4.0 base score

6.9Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 4.0	6.9

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/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: None
Vulnerable system availability: Low
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: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system 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 Vulnerable System 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 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 29 Oct 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 30 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

Affected software

Product	Affected	Fixed in
Homebrewkimi-cli`pkg:brew/kimi-cli`Other threats	Affected >=1.37.0	Fixed in–

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AI-suggested

The recommended fix is to validate the total input length against a maximum allowed size before performing the split operation. Until a patch is available, users should be aware that the size guard does not prevent memory allocation amplification during deserialization. Monitor vendor advisories for official fixes.

Description

joserfc 1.7.4 has a vulnerability in its compact JWS size guard where it allocates attacker-controlled segments before rejecting oversized inputs. This occurs because the library calls bytes.split() on the input before validating its size, causing an additional allocation roughly equal to the payload size. The issue leads to increased memory usage prior to rejection but does not prevent transport-layer large headers. The vulnerability has a CVSS 4.0 score of 6.9 (medium severity).

Impact

An attacker can cause the joserfc library to allocate memory roughly equal to the size of an attacker-controlled payload before rejecting it, potentially leading to increased memory consumption and possible denial of service due to memory exhaustion. However, the vulnerability does not allow bypassing size restrictions or direct exploitation beyond memory amplification. No known exploits in the wild have been reported.

Summary

The joserfc library version 1.7.4 defines limits on compact JWS header, payload, and signature sizes but performs a bytes.split() operation on the input before validating these limits. Since Python's bytes.split() copies the segments, this results in an attacker-controlled allocation approximately the size of the payload before the library rejects the input with an ExceededSizeError. This behavior undermines the intended allocation-limiting purpose of the size guard. The vulnerability does not affect transport-layer protections but allows memory amplification during deserialization. The recommended fix is to check the total input length before splitting and to use bounded find() operations or memory views to validate segment sizes before materializing them.

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Affected software

Description

AI analysisMachine-generated, updated 31 Oct 2026, 15:55 UTC

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