CVE-2026-27212: Prototype pollution in swiper

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 46: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 46% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.
• Only applies if your dependency tree includes swiper (npm) >= 6.5.1, < 12.1.2, fixed in 12.1.2. Check your lockfile, including transitive dependencies.

What it is

Swiper is a free and mobile touch slider with hardware accelerated transitions and native behavior. Versions 6.5.1 through 12.1.1 have a Prototype pollution vulnerability. The vulnerability resides in line 94 of shared/utils.mjs, where the indexOf() function is used to check whether user provided input contain forbidden strings. Despite a previous fix that attempted to mitigate prototype pollution by checking whether user input contained a forbidden key, it is still possible to pollute Object.prototype via a crafted input using Array.prototype. The exploit works across Windows and Linux and on Node and Bun runtimes. Any application that processes attacker-controlled input using this package may be affected by the following: Authentication Bypass, Denial of Service and RCE. This issue is fixed in version 12.1.2.

From the GitHub advisory

Summary A prototype pollution vulnerability exists in the the npm package swiper (>=6.5.1,

Details The vulnerability resides in line 94 of shared/utils.mjs where indexOf() function is used to check whether user provided input contain forbidden strings.

PoC Steps to reproduce 1. Install latest version of swiper using npm install 2. Run the following code snippet:

Expected behavior Prototype pollution should be prevented and {} should not gain new properties. This should be printed on the console:

Actual behavior Object.prototype is polluted This is printed on the console:

Weakness type: CWE-1321.

Product: swiper (npm) · Assigned by: GitHub_M · Published: 2026-02-21

Affected and fixed versions

Severity scores

• Attack vector: local access needed
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.57% probability of exploitation activity in the next 30 days; percentile 46.

Timeline

• 2026-02-19 — GitHub-reviewed advisory GHSA-hmx5-qpq5-p643 published (critical)
• 2026-02-21 — CVE record published by GitHub_M
• 2026-02-24 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-hmx5-qpq5-p643 github.com
2. CVE.org record CVE-2026-27212 cve.org
3. NVD entry CVE-2026-27212 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical npm advisories · Today’s Security Digest