CVE-2025-6499VulnerabilityPublished 23 Jun 2025

CVE-2025-6499: vstakhov libucl · Heap-based Buffer Overflow

Affects vstakhov libuclSource CVE Database V5

Not known to be exploited · CVSS 4.8 Medium.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 4.0 base score

4.8Medium

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 17% 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 2026-10-25.

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
GitHubvstakhov/libucl`pkg:github/vstakhov/libucl`Other threats	Affected =0.9.0 =0.9.1 =0.9.2	Fixed in–

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

AI-suggested

Identify all instances of libucl usage within your environment, including embedded systems, network appliances, and Linux-based servers.

Upgrade libucl to a version later than 0.9.2 once a patched release is available from the vendor or maintainers. Monitor official repositories and vendor advisories for patch announcements.

If immediate patching is not possible, restrict local access to systems running vulnerable libucl versions by enforcing strict access controls and limiting user privileges.

Implement application whitelisting and runtime protection mechanisms to detect and prevent anomalous behavior that could indicate exploitation attempts.

Conduct internal audits and penetration tests focusing on local privilege escalation and buffer overflow vectors to identify potential exploitation paths.

Educate system administrators and users about the risks of local exploitation and the importance of maintaining updated software components.

Consider deploying host-based intrusion detection systems (HIDS) that can monitor heap corruption or unusual process crashes related to libucl usage.

Isolate critical systems that use libucl in separate network segments to reduce the risk of lateral movement by attackers with local access.

Description

A vulnerability classified as problematic was found in vstakhov libucl up to 0.9.2. Affected by this vulnerability is the function ucl_parse_multiline_string of the file src/ucl_parser.c. The manipulation leads to heap-based buffer overflow. The attack needs to be approached locally. The exploit has been disclosed to the public and may be used.

Impact

For European organizations, the impact of CVE-2025-6499 depends largely on the deployment of libucl in their software stacks. Organizations using software that relies on libucl for configuration parsing—particularly in Linux-based environments, embedded systems, or network devices—may be vulnerable if they run affected versions. The local attack requirement limits the threat to insiders or attackers who have already gained some level of access to the system. However, successful exploitation could lead to denial of service through application crashes or potentially privilege escalation if combined with other vulnerabilities. This could disrupt critical services, especially in sectors relying heavily on Linux infrastructure such as telecommunications, finance, and government. The medium severity rating reflects moderate risk, but the public disclosure of the exploit code increases the urgency for mitigation. European organizations with strict security policies and segmented networks may contain the risk more effectively, but those with less controlled internal access or legacy systems may face higher exposure. The vulnerability does not directly compromise confidentiality or integrity but can affect availability and system stability.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 23 Jun 2025, 02:49 UTC

Technical details

References

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