CVE-2026-56306

Capgo - Subkey Enforcement Bypass via x-limited-key-id Header Parsing

Published Jun 22, 2026 CVSS 4.0 · 5.3 Medium EPSS < 1% KEV · Not listed

Description

Capgo before 12.128.2 contains a weak parsing vulnerability in the x-limited-key-id header that allows attackers to bypass subkey enforcement by submitting malformed values, zero, or duplicate headers that result in NaN or falsy values. Remote attackers can manipulate the x-limited-key-id header to disable limited key scoping and execute requests using the main API key context instead of restricted subkey permissions.

Analysis

Technical impact

The vulnerability is a weak parsing in the x‑limited‑key‑id header that allows an attacker to submit malformed, zero, or duplicate header values causing the server to treat the value as NaN or falsy. This bypasses the intended subkey enforcement so that requests are executed under the main API key context instead of the restricted subkey permissions, effectively elevating the attacker’s privileges.

Affected Systems

Capgo deployments running any version prior to 12.128.2 are affected. The only affected product is the Capgo server component; newer releases are not impacted.

Risk and Exploitability

The CVSS score of 5.3 indicates moderate risk. EPSS data is unavailable and the vulnerability is not listed in the CISA KEV catalog. Attackers can trigger the flaw over the network by sending a crafted HTTP request with a malicious x‑limited‑key‑id header, enabling them to use the main API key and access sensitive data or services.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Capgo

unaffected

Version	Status	Constraints
`0`	affected	< 12.128.2
`12.128.2`	unaffected	—

No data.

Vendor Product Versions

Cap-go

Version	Status	Scheme	Platform
`[0,12.128.2)`	affected	semver	—
`12.128.2`	unaffected	semver	—

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade Capgo to version 12.128.2 or later to apply the header parsing fix.
As a temporary measure, enforce strict validation of the x‑limited‑key‑id header on any reverse proxy or frontend, rejecting malformed, zero‑length, or duplicate values before they reach the Capgo backend.
Monitor API access logs for sudden or unexpected use of the main API key and configure alerting to detect potential abuse of subkey enforcement bypass.

Generated by OpenCVE AI on June 22, 2026 at 23:38 UTC.

Tracking

Advisories

No advisories available

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact Low

Vulnerable System Integrity Impact Low

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact Low

Subsequent System Integrity Impact Low

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required Low

Scope Changed

Confidentiality Impact Low

Integrity Impact Low

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.302% probability within 30 days)

Exploitation poc

Automatable no

Technical Impact partial

References

Link	Providers
https://github.com/Cap-go/capgo/security/advisories/GHSA-42vv-8j94-24wj
https://www.vulncheck.com/advisories/capgo-subkey-enforcement-bypass-via-x-limited-key-id-header-parsing

History

Jun 24, 2026 4:45 PM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Cap-go Cap-go cap-go
Vendors & Products		Cap-go Cap-go cap-go

Jun 23, 2026 1:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Jun 22, 2026 10:00 PM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Description		Capgo before 12.128.2 contains a weak parsing vulnerability in the x-limited-key-id header that allows attackers to bypass subkey enforcement by submitting malformed values, zero, or duplicate headers that result in NaN or falsy values. Remote attackers can manipulate the x-limited-key-id header to disable limited key scoping and execute requests using the main API key context instead of restricted subkey permissions.
Title		Capgo - Subkey Enforcement Bypass via x-limited-key-id Header Parsing
Weaknesses		CWE-20
References		https://github.com/Cap-go/capgo/security/advisories/GHSA-42vv-8j94-24wj https://www.vulncheck.com/advisories/capgo-subkey-enforcement-bypass-via-x-limited-key-id-header-parsing
Metrics		cvssV3_1 `{'score': 6.4, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N'}` cvssV4_0 `{'score': 5.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N'}`