CVE-2025-6497VulnerabilityPublished 23 Jun 2025

CVE-2025-6497: HTACG tidy-html5 · Reachable Assertion

Affects HTACG tidy-html5Source CVE Database V5

Not known to be exploited · CVSS 4.8 Medium.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 4.0 base score

4.8Medium

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

EPSS: 0.1% chance of exploitation in 30 days – higher than 5% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Base metrics

Attack Vector: Local
Attack Complexity: Low
Attack Requirements: None
Privileges Required: Low
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
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: Local: The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
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: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to 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 23 Jun 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
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), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.

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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC 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
GitHubhtacg/tidy-html5`pkg:github/htacg/tidy-html5`Other threats	Affected =5.8.0	Fixed in–

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AI-suggested

1. Upgrade tidy-html5: The most effective mitigation is to update tidy-html5 to a version later than 5.8.0 where this vulnerability is patched. Monitor HTACG project releases and apply updates promptly. 2. Restrict local access: Limit local user privileges and access to systems running tidy-html5 to trusted personnel only, reducing the risk of local exploitation. 3. Implement input validation: Where possible, validate or sanitize HTML input before it reaches tidy-html5 to prevent malformed namespace data that triggers the assertion. 4. Use sandboxing: Run tidy-html5 processes in isolated environments or containers to contain potential crashes and prevent impact on critical systems. 5. Monitor logs and crashes: Implement monitoring to detect abnormal termination or crashes of tidy-html5 processes, enabling rapid response to exploitation attempts. 6. Review embedding applications: Audit applications embedding tidy-html5 to ensure they handle failures gracefully and do not expose additional attack surfaces. 7. Incident response readiness: Prepare internal teams to respond to potential denial of service incidents related to this vulnerability, including rollback plans and patch deployment procedures.

Description

A vulnerability was found in HTACG tidy-html5 5.8.0. It has been rated as problematic. This issue affects the function prvTidyParseNamespace of the file src/parser.c. The manipulation leads to reachable assertion. Attacking locally is a requirement. The exploit has been disclosed to the public and may be used.

Impact

For European organizations, the primary impact of CVE-2025-6497 is a potential denial of service (DoS) condition on systems that utilize tidy-html5 5.8.0 locally. This could disrupt internal development environments, automated content sanitization processes, or any service embedding tidy-html5 for HTML parsing. While the vulnerability does not allow remote code execution or data exfiltration, the availability impact could affect productivity and service reliability, especially in organizations with automated pipelines for web content processing. Sectors relying heavily on web content management, such as media, publishing, and e-commerce, may experience operational disruptions if affected systems are exploited. Additionally, organizations with strict uptime requirements or those using tidy-html5 in security-sensitive sanitization contexts might face increased risk of service interruptions. Given the local attack vector, insider threats or compromised internal systems pose the most likely exploitation scenario. The lack of known exploits in the wild reduces immediate risk but the public disclosure means attackers could develop exploits targeting vulnerable installations. European organizations should assess their use of tidy-html5 5.8.0 in local environments and embedded applications to understand exposure.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 23 Jun 2025, 01:04 UTC

Technical details

References

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