VulnerabilityPublished 20 Mar 2026Updated 24 Mar 2026

CVE-2026-4494: atjiu pybbs · Cross-site Scripting

Affects atjiu pybbsSource CVE Database V5

Compare

Public exploit available · CVSS 5.1 Medium.

Data as of 1 Nov 2026, 11:03 UTC

CVSS 4.0 base score

5.1Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 22% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: Low
User Interaction: Passive
Vulnerable system confidentiality: None
Vulnerable system integrity: Low
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: 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: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to 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 20 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 1 Nov 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
atjiupybbs	Affected =6.0.0	Fixed in–
Mavenco.yiiu/pybbs`pkg:maven/co.yiiu/pybbs`Other threats	Affected =6.0.0	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2026-4494, organizations should first upgrade pybbs to a version where this vulnerability is patched once available. In the absence of a patch, implement strict input validation and sanitization on all user inputs handled by the create function in TopicApiController.java, ensuring that any HTML or script tags are properly escaped or removed. Employ output encoding techniques when rendering user-generated content to prevent script execution in browsers. Utilize Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts. Limit the exposure of the vulnerable API endpoint by enforcing authentication and authorization controls where possible. Monitor web application logs for suspicious input patterns indicative of XSS attempts. Educate users about the risks of clicking on untrusted links or content within the forum. Finally, conduct regular security assessments and code reviews focusing on input handling and output rendering to prevent similar vulnerabilities.

Description

A vulnerability was identified in atjiu pybbs 6.0.0. This affects the function create of the file src/main/java/co/yiiu/pybbs/controller/api/TopicApiController.java. The manipulation leads to cross site scripting. It is possible to initiate the attack remotely. The exploit is publicly available and might be used.

Impact

The primary impact of CVE-2026-4494 is the potential compromise of user confidentiality and integrity through cross-site scripting attacks. Attackers can execute arbitrary scripts in victims' browsers, potentially stealing session cookies, redirecting users to malicious sites, or manipulating displayed content. This can lead to account takeover, phishing, or reputational damage for organizations running vulnerable pybbs instances. Since the vulnerability is remotely exploitable without authentication, any exposed pybbs 6.0.0 installation accessible over the internet is at risk. The requirement for user interaction limits automated exploitation but does not eliminate risk, especially in social engineering scenarios. The scope is limited to the affected pybbs version and its user base, but given the public availability of exploits, the threat could escalate if not addressed. Organizations relying on pybbs for community forums or discussions may face user trust erosion and potential data leakage if exploited.

References

Community reviews

Loading reviews…

Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Mar 2026, 22:42 UTC

Technical details

References

Community reviews

Related threats