# Echo vulnerable to Reflected Cross-Site Scripting (XSS) via unsanitized JSONP callback in Context.JSONP / Context.JSONPBlob Advisory record · `GHSA-h9g5-28mm-hx3g` - **Identifiers:** `GHSA-h9g5-28mm-hx3g` · `CVE-2026-118652` · `GO-2026-6876` - **State:** Confirmed - **Severity:** CVSS 6.1 Medium - **Critical:** No - **Weakness (CWE):** [CWE-79](https://cwe.mitre.org/data/definitions/79.html) - **Tags:** [Cross-site scripting (XSS)](https://agentprime.io/advisories/tag/xss.md) - **Published:** 28 Oct 2026 - **Updated:** 5 Nov 2026 - **Reviewed by a person:** No Published by the GitHub Advisory Database at 28 Oct 2026, 19:54 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. ## Affected packages - `github.com/labstack/echo/v5` (Go): affected `<5.4.0`; fixed in `5.4.0` - `github.com/labstack/echo/v4` (Go): affected `<4.16.0`; fixed in `4.16.0` ## Machine-written summary Summary written by Claude Haiku from the source advisory. Not reviewed by a person. > Echo v5 before 5.4.0 and Echo v4 before 4.16.0 do not validate the callback parameter in Context.JSONP and Context.JSONPBlob, so a callback supplied by an attacker is written into the JavaScript response unchanged. An attacker can get a victim to open a crafted link, which can run arbitrary JavaScript in the victim's browser session on the affected site. Upgrade to github.com/labstack/echo/v5 5.4.0 or github.com/labstack/echo/v4 4.16.0; the fixed versions accept only identifier-style callbacks and return 400 otherwise. Written 1 Nov 2026. ## Not analysed yet We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check. ## Severity and exploitation - 6.1 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`, from CNA (GitHub_M) - **CISA KEV:** Not listed. - **EPSS:** 0.0024, the 15th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days. ## Timeline - 28 Oct 2026, 19:35 UTC: [Confirmed by the CVE List](https://www.cve.org/CVERecord?id=CVE-2026-118652) - 28 Oct 2026, 20:17 UTC: [Confirmed by NVD](https://nvd.nist.gov/vuln/detail/CVE-2026-118652) - 31 Oct 2026, 14:11 UTC: First seen by agentprime - 31 Oct 2026, 14:11 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-h9g5-28mm-hx3g) ## Sources - [GitHub Advisory Database: GHSA-h9g5-28mm-hx3g](https://github.com/advisories/GHSA-h9g5-28mm-hx3g) - [OSV: GHSA-h9g5-28mm-hx3g](https://osv.dev/vulnerability/GHSA-h9g5-28mm-hx3g) - - - - - - Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code. ## Check whether this affects you A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet. - With the agentprime MCP server (), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: - In a browser: reads your lockfile in the browser, never uploading it. - Whether it touches your code, with file and line: the Claude Code plugin, - As JSON: , or `POST https://api.agentprime.io/v1/match` with your packages () --- The web page: . Everything for agents: .