CVE-2026-25635

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{"bugzilla": {"description": "calibre: Calibre: Remote Code Execution via path traversal in CHM reader", "id": "2437936", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2437936"}, "csaw": false, "cvss3": {"cvss3_base_score": "8.6", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H", "status": "draft"}, "details": ["calibre is an e-book manager. Prior to 9.2.0, Calibre's CHM reader contains a path traversal vulnerability that allows arbitrary file writes anywhere the user has write permissions. On Windows (haven't tested on other OS's), this can lead to Remote Code Execution by writing a payload to the Startup folder, which executes on next login. This vulnerability is fixed in 9.2.0.", "A flaw was found in Calibre's CHM reader. This path traversal vulnerability allows an attacker to write arbitrary files to locations where the user has write permissions. On Windows systems, this could lead to remote code execution by placing a malicious file in the Startup folder, which would then execute upon the user's next login. This vulnerability primarily results in arbitrary code execution."], "mitigation": {"lang": "en:us", "value": "Users should avoid opening untrusted CHM files with Calibre. This operational control reduces the risk of exploitation by preventing the processing of malicious content."}, "name": "CVE-2026-25635", "public_date": "2026-02-06T20:10:29Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-25635\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-25635\nhttps://github.com/kovidgoyal/calibre/commit/9739232fcb029ac15dfe52ccd4fdb4a07ebb6ce9\nhttps://github.com/kovidgoyal/calibre/security/advisories/GHSA-32vh-whvh-9fxr"], "statement": "This IMPORTANT flaw in Calibre's CHM reader allows an attacker to perform path traversal, leading to arbitrary file writes. This could enable an attacker to write malicious files to arbitrary locations on the filesystem where the user has write permissions. Exploitation requires a user to open a specially crafted CHM file.", "threat_severity": "Important"}

{"analysis": {"en": {"generated_at": "2026-04-18T13:29:04.213295+00:00", "value": {"mitigation_remediation": ["Upgrade Calibre to version 9.2.0 or later to eliminate the path traversal flaw.", "Avoid opening CHM files from untrusted or unknown sources; treat all CHM content as potentially malicious.", "Restrict the user account that runs Calibre so it cannot write to system startup directories\u2014or disable automatic execution of programs placed in the Startup folder."], "summary": {"action": "Immediate Patch", "impact": "Remote Code Execution"}, "threat_synthesis": {"affected_systems": "The vulnerable product is Calibre developed by Kovid Goyal. The issue is present in all releases prior to version 9.2.0. Users running any of those versions on operating systems that allow write access to arbitrary directories are at risk. The software appears in the Calibre\u2011ebook vendor entry in the Common Platform Enumeration database.", "description_and_impact": "Calibre, an e\u2011book manager, contains a path traversal flaw in its CHM reader that permits arbitrary file writes when a user opens a malicious CHM file. The weakness allows an attacker to place files, such as a malicious executable, in any location where the user has write permission. On Windows, an attacker can write a payload into the Startup folder, causing the payload to be executed the next time the user logs in. This vulnerability results in full code execution on the victim\u2019s machine and disrupts system security and integrity. The weakness is classified as CWE\u201122.", "risk_and_exploitability": "Based on the description, the likely attack vector is the local or remote delivery of a crafted CHM file, such as through phishing or compromised content stores. Once the file is parsed by Calibre, the attacker can write to locations under the user\u2019s privilege. On Windows this enables remote code execution by persisting a payload in the Startup folder. The CVSS score of 8.6 signals a high severity of this flaw, while the EPSS score of less than 1\u202f% indicates a low probability that the vulnerability will be actively exploited in the near term. The vulnerability has not yet appeared in the CISA KEV catalogue, so there are no publicly reported active exploits, but the high CVSS warrants proactive mitigation."}}}}, "created": "2026-02-09T10:50:15.148904+00:00", "updated": "2026-04-18T13:30:45.751799+00:00", "vendors": ["kovidgoyal", "kovidgoyal$PRODUCT$calibre"]}