CVE-2026-2391VulnerabilityPublished 12 Feb 2026

CVE-2026-2391: qs · Improper Input Validation

Affects qsSource CVE Database V5

Mentioned vulnerabilities

CVE-2025-15284

Not known to be exploited · CVSS 6.3 Medium · fixed in 6.14.1 : update qs when convenient.

Data as of 26 Oct 2026, 08:30 UTC

CVSS 4.0 base score

6.3Medium

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

EPSS: 0.5% chance of exploitation in 30 days – higher than 45% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 6.14.1

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
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

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: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
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: 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.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 12 Feb 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 26 Oct 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.
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
npmqs`pkg:npm/qs`Other threats	Affected >=6.7.0 <=6.14.1	Fixed in–

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AI-suggested

1. Upgrade the qs library to a version where this vulnerability is patched once available. 2. If upgrading is not immediately possible, disable the comma option in qs configuration to prevent parsing comma-separated values as arrays. 3. Implement custom input validation and sanitization on query parameters before passing them to qs, limiting the length and format of inputs to prevent excessive commas or large arrays. 4. Employ web application firewalls (WAFs) or API gateways to detect and block suspicious query parameters with abnormally large numbers of commas or excessively long values. 5. Monitor application logs and memory usage for signs of abnormal resource consumption that could indicate exploitation attempts. 6. Consider rate limiting or throttling requests with large query strings to reduce the risk of DoS. 7. Review and test application error handling to ensure graceful degradation in case of parsing failures. 8. Educate development teams about secure configuration of third-party libraries and the risks of enabling non-default options without proper validation.

Description

### Summary The `arrayLimit` option in qs does not enforce limits for comma-separated values when `comma: true` is enabled, allowing attackers to cause denial-of-service via memory exhaustion. This is a bypass of the array limit enforcement, similar to the bracket notation bypass addressed in GHSA-6rw7-vpxm-498p (CVE-2025-15284). ### Details When the `comma` option is set to `true` (not the default, but configurable in applications), qs allows parsing comma-separated strings as arrays (e.g., `?param=a,b,c` becomes `['a', 'b', 'c']`). However, the limit check for `arrayLimit` (default: 20) and the optional throwOnLimitExceeded occur after the comma-handling logic in `parseArrayValue`, enabling a bypass. This permits creation of arbitrarily large arrays from a single parameter, leading to excessive memory allocation. **Vulnerable code** (lib/parse.js: lines ~40-50): ```js if (val && typeof val === 'string' && options.comma && val.indexOf(',') > -1) { return val.split(','); } if (options.throwOnLimitExceeded && currentArrayLength >= options.arrayLimit) { throw new RangeError('Array limit exceeded. Only ' + options.arrayLimit + ' element' + (options.arrayLimit === 1 ? '' : 's') + ' allowed in an array.'); } return val; ``` The `split(',')` returns the array immediately, skipping the subsequent limit check. Downstream merging via `utils.combine` does not prevent allocation, even if it marks overflows for sparse arrays.This discrepancy allows attackers to send a single parameter with millions of commas (e.g., `?param=,,,,,,,,...`), allocating massive arrays in memory without triggering limits. It bypasses the intent of `arrayLimit`, which is enforced correctly for indexed (`a[0]=`) and bracket (`a[]=`) notations (the latter fixed in v6.14.1 per GHSA-6rw7-vpxm-498p). ### PoC **Test 1 - Basic bypass:** ``` npm install qs ``` ```js const qs = require('qs'); const payload = 'a=' + ','.repeat(25); // 26 elements after split (bypasses arrayLimit: 5) const options = { comma: true, arrayLimit: 5, throwOnLimitExceeded: true }; try { const result = qs.parse(payload, options); console.log(result.a.length); // Outputs: 26 (bypass successful) } catch (e) { console.log('Limit enforced:', e.message); // Not thrown } ``` **Configuration:** - `comma: true` - `arrayLimit: 5` - `throwOnLimitExceeded: true` Expected: Throws "Array limit exceeded" error. Actual: Parses successfully, creating an array of length 26. ### Impact Denial of Service (DoS) via memory exhaustion.

Impact

The primary impact of CVE-2026-2391 is denial-of-service (DoS) through memory exhaustion. Attackers can send specially crafted HTTP requests with query parameters containing extremely long comma-separated lists, causing the qs parser to allocate large arrays in memory. This can lead to application crashes, degraded performance, or complete service outages. Organizations running web applications or APIs that use the vulnerable qs version with comma parsing enabled are at risk. The vulnerability can be exploited remotely without authentication or user interaction, increasing its risk profile. While it does not directly compromise confidentiality or integrity, the availability impact can disrupt business operations, especially for high-traffic or resource-constrained environments. This may affect cloud services, SaaS platforms, and internal applications relying on qs for query string parsing. The lack of enforcement of array limits also increases the risk of resource exhaustion attacks at scale, potentially amplifying the impact in distributed denial-of-service (DDoS) scenarios. No known exploits in the wild have been reported yet, but the vulnerability is straightforward to trigger, making it a credible threat.

Summary

CVE-2026-2391 is a vulnerability in the qs JavaScript library version 6.7.0 related to improper input validation (CWE-20). The issue occurs when the qs parser is configured with the comma option set to true, which allows parsing comma-separated strings into arrays. The arrayLimit option is intended to restrict the maximum number of elements in parsed arrays to prevent resource exhaustion. However, the limit enforcement happens after the comma-splitting logic in the parseArrayValue function. Specifically, when a string containing commas is split into an array, the function returns immediately without checking if the resulting array exceeds the configured arrayLimit. This bypasses the limit check, allowing attackers to craft a single query parameter with millions of commas, resulting in the allocation of very large arrays in memory. The downstream merging logic does not prevent this excessive allocation, leading to potential denial-of-service via memory exhaustion. This vulnerability is similar to a previously fixed issue (CVE-2025-15284) involving bracket notation bypasses but affects the comma parsing feature instead. The vulnerability does not require authentication or user interaction and can be triggered remotely by sending maliciously crafted HTTP requests. The default configuration of qs does not enable the comma option, so only applications explicitly enabling it are vulnerable. The CVSS 4.0 base score is 6.3 (medium), reflecting network attack vector, low complexity, no privileges or user interaction required, and limited impact on availability via memory exhaustion.

CWE-20Improper Input Validation (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #18OWASP Top 10 A05:2025: Injection (opens in a new tab)
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Architecture and Design · Attack Surface Reduction
Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build "recognizers" for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of…
Architecture and Design · Libraries or Frameworks
Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
Architecture and Design · Implementation · Attack Surface Reduction
Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any…
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
Injection Prevention (opens in a new tab)
SQL Injection Prevention (opens in a new tab)
Injection Prevention in Java (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Buffer Overflow via Environment Variables (opens in a new tab)
Server Side Include (SSI) Injection (opens in a new tab)
Cross Zone Scripting (opens in a new tab)
Command Line Execution through SQL Injection (opens in a new tab)
Object Relational Mapping Injection (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 19 Feb 2026, 14:02 UTC

WeaknessesCWE-20

Technical details

References

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