VulnerabilityPublished 20 Mar 2026

CVE-2026-4495: atjiu pybbs · Cross-site Scripting

Affects atjiu pybbsSource CVE Database V5

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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: 0.2% chance of exploitation in 30 days – higher than 19% 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–
Mavenatjiu/pybbs`pkg:maven/atjiu/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

Immediate mitigation should include implementing strict input validation on all user-supplied data in the comment creation API to reject or sanitize potentially malicious scripts.
Apply proper output encoding (e.g., HTML entity encoding) when rendering user comments to prevent script execution in browsers.
Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts on web pages.
Monitor web application logs for suspicious comment submissions or unusual user activity indicative of exploitation attempts.
If possible, isolate the comment functionality or restrict comment posting privileges temporarily until a patch is available.
Engage with the vendor or community to obtain or develop an official patch addressing the root cause.
Educate users about the risks of clicking on suspicious links or interacting with untrusted content within the forum.
Regularly update and audit the pybbs installation and dependencies to detect and remediate similar vulnerabilities proactively.

Description

CVE-2026-4495 is a medium severity cross-site scripting (XSS) vulnerability found in atjiu pybbs version 6.0.0, specifically in the create function of CommentApiController.java. The flaw allows remote attackers to inject malicious scripts without requiring authentication, though user interaction is needed to trigger the payload. Exploit code has been publicly released, increasing the risk of exploitation. This vulnerability can lead to theft of user credentials, session hijacking, and unauthorized actions performed in the context of a victim user. No official patch is currently available, so mitigation relies on input validation and output encoding. Organizations using pybbs 6.0.

Impact

The primary impact of CVE-2026-4495 is the compromise of user trust and security through cross-site scripting attacks. Successful exploitation can lead to theft of session cookies, enabling attackers to impersonate legitimate users and perform unauthorized actions. This can result in data leakage, unauthorized content posting, or manipulation of user accounts. For organizations, this can damage reputation, lead to user attrition, and potentially expose sensitive user information. While the vulnerability does not directly compromise server confidentiality or availability, the indirect effects of XSS attacks can disrupt normal operations and user interactions. The public availability of exploit code increases the risk of widespread attacks, especially on unpatched or poorly monitored pybbs installations. Organizations with active online communities using pybbs 6.0.0 are at risk of targeted or opportunistic attacks, potentially affecting millions of users worldwide.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Mar 2026, 19:32 UTC

Technical details

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