VulnerabilityPublished 11 Mar 2026

CVE-2026-3963: perfree go-fastdfs-web · Use of Hard-coded Cryptographic Key

Affects perfree go-fastdfs-webSource CVE Database V5

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Public exploit available · CVSS 6.3 Medium.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score

6.3Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 30% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: High
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: Low
Vulnerable system integrity: None
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

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: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
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: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within 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.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CVSS exploit maturity: proof of concept public
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), CVSS vector, 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
perfreego-fastdfs-web	Affected 1.3.0 – 1.3.7 8 affected builds	Fixed in–

AI-suggested

Given the absence of official patches, organizations should take immediate steps to mitigate risk. First, disable the RememberMe feature in go-fastdfs-web configurations to prevent use of the vulnerable cryptographic key. If disabling is not feasible, consider implementing custom cryptographic key management to replace the hard-coded key with a securely generated and stored key. Network-level controls such as web application firewalls (WAFs) can be configured to monitor and block suspicious requests targeting authentication tokens. Conduct thorough audits of authentication logs to detect anomalous session activity indicative of token manipulation. Limit exposure by restricting access to the go-fastdfs-web interface to trusted networks or VPNs. Monitor vendor channels for updates or patches and plan for timely application once available. Additionally, consider deploying multi-factor authentication (MFA) on affected systems to reduce the impact of compromised tokens. Finally, educate users and administrators about the risks and signs of session hijacking to improve incident response readiness.

Description

CVE-2026-3963 is a medium severity vulnerability in perfree go-fastdfs-web versions up to 1.3.7, involving the use of a hard-coded cryptographic key in the Apache Shiro RememberMe component. The flaw exists in the rememberMeManager function within ShiroConfig.java, allowing remote attackers to potentially exploit the hard-coded key. Exploitation complexity is high and no user interaction or privileges are required, but the exploitability is considered difficult. Although a public exploit exists, no known widespread attacks have been reported. The vendor has not responded to disclosure attempts, and no patches are currently available. Organizations using affected versions should prioritize mitigation to prevent potential compromise of authentication tokens and session integrity.

Impact

The primary impact of this vulnerability is the potential compromise of user authentication tokens managed by the Apache Shiro RememberMe feature. Attackers who successfully exploit this flaw could decrypt or forge RememberMe cookies, leading to unauthorized access to user sessions without needing valid credentials. This could result in unauthorized data access, privilege escalation, and potential lateral movement within affected environments. Since the vulnerability affects a web-based distributed file system management tool (go-fastdfs-web), attackers might gain access to sensitive file storage or management functions. The medium severity score reflects that while exploitation is difficult, the consequences of a successful attack could be significant, especially in environments where go-fastdfs-web is used to manage critical data or infrastructure. The lack of vendor response and patches increases the risk exposure timeframe. Organizations relying on this software may face increased risk of data breaches, session hijacking, and loss of trust in authentication mechanisms.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 19 Mar 2026, 02:33 UTC

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