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Vulnerability Details :

CVE-2026-27824

Summary
Assigner-GitHub_M
Assigner Org ID-a0819718-46f1-4df5-94e2-005712e83aaa
Published At-27 Feb, 2026 | 19:46
Updated At-27 Feb, 2026 | 19:46
Rejected At-
Credits

calibre has IP Ban Bypass via X-Forwarded-For Header Spoofing

calibre is a cross-platform e-book manager for viewing, converting, editing, and cataloging e-books. Prior to version 9.4.0, the calibre Content Server's brute-force protection mechanism uses a ban key derived from both `remote_addr` and the `X-Forwarded-For` header. Since the `X-Forwarded-For` header is read directly from the HTTP request without any validation or trusted-proxy configuration, an attacker can bypass IP-based bans by simply changing or adding this header, rendering the brute-force protection completely ineffective. This is particularly dangerous for calibre servers exposed to the internet, where brute-force protection is the primary defense against credential stuffing and password guessing attacks. Version 9.4.0 contains a fix for the issue.

Vendors
-
Not available
Products
-
Metrics (CVSS)
VersionBase scoreBase severityVector
Weaknesses
Attack Patterns
Solution/Workaround
References
HyperlinkResource Type
EPSS History
Score
Latest Score
-
N/A
No data available for selected date range
Percentile
Latest Percentile
-
N/A
No data available for selected date range
Stakeholder-Specific Vulnerability Categorization (SSVC)
▼Common Vulnerabilities and Exposures (CVE)
cve.org
Assigner:GitHub_M
Assigner Org ID:a0819718-46f1-4df5-94e2-005712e83aaa
Published At:27 Feb, 2026 | 19:46
Updated At:27 Feb, 2026 | 19:46
Rejected At:
▼CVE Numbering Authority (CNA)
calibre has IP Ban Bypass via X-Forwarded-For Header Spoofing

calibre is a cross-platform e-book manager for viewing, converting, editing, and cataloging e-books. Prior to version 9.4.0, the calibre Content Server's brute-force protection mechanism uses a ban key derived from both `remote_addr` and the `X-Forwarded-For` header. Since the `X-Forwarded-For` header is read directly from the HTTP request without any validation or trusted-proxy configuration, an attacker can bypass IP-based bans by simply changing or adding this header, rendering the brute-force protection completely ineffective. This is particularly dangerous for calibre servers exposed to the internet, where brute-force protection is the primary defense against credential stuffing and password guessing attacks. Version 9.4.0 contains a fix for the issue.

Affected Products
Vendor
kovidgoyal
Product
calibre
Versions
Affected
  • < 9.4.0
Problem Types
TypeCWE IDDescription
CWECWE-307CWE-307: Improper Restriction of Excessive Authentication Attempts
CWECWE-346CWE-346: Origin Validation Error
Type: CWE
CWE ID: CWE-307
Description: CWE-307: Improper Restriction of Excessive Authentication Attempts
Type: CWE
CWE ID: CWE-346
Description: CWE-346: Origin Validation Error
Metrics
VersionBase scoreBase severityVector
3.15.3MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Version: 3.1
Base score: 5.3
Base severity: MEDIUM
Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Metrics Other Info
Impacts
CAPEC IDDescription
Solutions
Configurations
Workarounds
Exploits
Credits
Timeline
EventDate
Replaced By
Rejected Reason
References
HyperlinkResource
https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw
x_refsource_CONFIRM
Hyperlink: https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw
Resource:
x_refsource_CONFIRM
Information is not available yet
▼National Vulnerability Database (NVD)
nvd.nist.gov
Source:security-advisories@github.com
Published At:27 Feb, 2026 | 20:21
Updated At:27 Feb, 2026 | 20:21

calibre is a cross-platform e-book manager for viewing, converting, editing, and cataloging e-books. Prior to version 9.4.0, the calibre Content Server's brute-force protection mechanism uses a ban key derived from both `remote_addr` and the `X-Forwarded-For` header. Since the `X-Forwarded-For` header is read directly from the HTTP request without any validation or trusted-proxy configuration, an attacker can bypass IP-based bans by simply changing or adding this header, rendering the brute-force protection completely ineffective. This is particularly dangerous for calibre servers exposed to the internet, where brute-force protection is the primary defense against credential stuffing and password guessing attacks. Version 9.4.0 contains a fix for the issue.

CISA Catalog
Date AddedDue DateVulnerability NameRequired Action
N/A
Date Added: N/A
Due Date: N/A
Vulnerability Name: N/A
Required Action: N/A
Metrics
TypeVersionBase scoreBase severityVector
Secondary3.15.3MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Type: Secondary
Version: 3.1
Base score: 5.3
Base severity: MEDIUM
Vector:
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
CPE Matches
Weaknesses
CWE IDTypeSource
CWE-307Primarysecurity-advisories@github.com
CWE-346Primarysecurity-advisories@github.com
CWE ID: CWE-307
Type: Primary
Source: security-advisories@github.com
CWE ID: CWE-346
Type: Primary
Source: security-advisories@github.com
Evaluator Description
Evaluator Impact

Evaluator Solution

Vendor Statements
References
HyperlinkSourceResource
https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrwsecurity-advisories@github.com
N/A
Hyperlink: https://github.com/kovidgoyal/calibre/security/advisories/GHSA-vhxc-r7v8-2xrw
Source: security-advisories@github.com
Resource: N/A

Change History

0
Information is not available yet

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