CVE-2026-0821VulnerabilityPublished 10 Jan 2026Updated 23 Feb 2026

CVE-2026-0821: quickjs · Heap-based Buffer Overflow

Affects quickjsSource CVE Database V5

Not known to be exploited · CVSS 6.9 Medium.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 4.0 base score

6.9Medium

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

EPSS: 0.5% chance of exploitation in 30 days – higher than 43% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: Low
Vulnerable system integrity: Low
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: 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: 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: 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: 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 10 Jan 2026
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
quickjs-ngquickjs	Affected =0.1 =0.2 =0.3 =0.4 =0.5 =0.6 =0.7 =0.8 =0.9 =0.10 =0.11.0	Fixed in–
GitHubquickjs-ng/quickjs`pkg:github/quickjs-ng/quickjs`Other threats	Affected =0.1 =0.2 =0.3 =0.4 =0.5 =0.6 =0.7 =0.8 =0.9 =0.10 =0.11.0	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-2026-0821, organizations should promptly apply the official patch identified by commit c5d80831e51e48a83eab16ea867be87f091783c5 to all affected quickjs versions up to 0.11.0. If immediate patching is not feasible, consider isolating or restricting network access to systems running vulnerable quickjs versions to reduce exposure. Employ runtime protections such as heap memory protection mechanisms (e.g., ASLR, DEP) and enable compiler-based mitigations like stack canaries and bounds checking where possible. Conduct thorough code audits for any custom integrations of quickjs to identify and remediate unsafe usage patterns. Monitor network traffic and logs for anomalous behavior indicative of exploitation attempts targeting the js_typed_array_constructor function. Finally, maintain an inventory of all devices and software components using quickjs to ensure comprehensive coverage of remediation efforts.

Description

A vulnerability was determined in quickjs-ng quickjs up to 0.11.0. This vulnerability affects the function js_typed_array_constructor of the file quickjs.c. Executing a manipulation can lead to heap-based buffer overflow. The attack may be launched remotely. The exploit has been publicly disclosed and may be utilized. This patch is called c5d80831e51e48a83eab16ea867be87f091783c5. A patch should be applied to remediate this issue.

Impact

The heap-based buffer overflow in quickjs-ng quickjs can have serious consequences for organizations worldwide. Exploitation could lead to arbitrary code execution, allowing attackers to take control of affected systems, steal sensitive data, or disrupt services. Denial of service attacks could also be launched, impacting availability. Since the vulnerability can be exploited remotely without authentication or user interaction, exposed systems are at significant risk. This is particularly concerning for embedded devices, IoT products, and software platforms that integrate quickjs for scripting capabilities. Organizations relying on quickjs in critical infrastructure or consumer devices may face operational disruptions, data breaches, or reputational damage. The medium severity rating indicates a notable but not critical risk, yet the ease of exploitation and broad usage of quickjs warrant urgent attention to patching and mitigation.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 23 Feb 2026, 22:44 UTC

Technical details

References

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