# CVE-2026-78661: Avoid quadratic complexity when coalescing text nodes in html in golang.org/x/net

Status: published. Published: 2026-10-27. Updated: 2026-11-04.

When coalescing adjacent text nodes in addText and fosterParent, appending to an existing TextNode's Data via string concatenation (n.Data += text) reallocated and copied the accumulated string on every token. Inputs containing many short text runs separated by ignored end tags (such as "a</x>") caused O(n^2) allocations and byte copies. Accumulate coalesced text in per-node byte slices during parsing and materialize Data strings once at the end of parse.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- golang.org/x/net / golang.org/x/net/html (golang.org/x/net/html): ≥ 0; < 0.62.0 (affected, semver). Source: CNA: Go

## Severity and prioritization

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N; source: ADP: CISA-ADP

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N; source: NVD: 134c704f-9b21-4f2e-91b3-4a467353bcc0

- CISA KEV: No listing in collected sources

- EPSS: 0.18% as of 2026-11-04; percentile 8.14%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-407

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://go.dev/cl/849365 (CNA: Go)

- https://go.dev/issue/82224 (CNA: Go)

- https://groups.google.com/g/golang-announce/c/sqrs2vTx_Xs (CNA: Go)

- https://pkg.go.dev/vuln/GO-2026-6860 (CNA: Go)

- https://go.dev/cl/849365 (security@golang.org)

- https://go.dev/issue/82224 (security@golang.org)

- https://groups.google.com/g/golang-announce/c/sqrs2vTx_Xs (security@golang.org)

- https://pkg.go.dev/vuln/GO-2026-6860 (security@golang.org)

## Provenance

- CNA: Go: https://www.cve.org/CVERecord?id=CVE-2026-78661; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-78661; retrieved 2026-11-04; source updated 2026-11-04

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-78661; retrieved 2026-11-04; source updated Not reported

Revision: bd9c9d6c9f5a7ccbf62693d0165ebd8be27b08fba1e219733a8d11d5486c8a50

Canonical: https://y2.dev/cve/CVE-2026-78661

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.