# CVE-2026-115700: SSRF allowlist bypass via percent-encoded bracketed IPv6 or trailing-dot IP literal in hackney

Status: published. Published: 2026-10-26. Updated: 2026-11-02.

Interpretation Conflict vulnerability in hackney_url in benoitc hackney allows Server Side Request Forgery via a percent-encoded bracketed IPv6 literal or an IP literal with a trailing dot. A host such as %5B%3A%3Affff%3A127%2E0%2E0%2E1%5D (decoding to [::ffff:127.0.0.1]) or 127.0.0.1. is not an IP address to a caller's allowlist built on uri_string:parse/1 and inet:parse_address/1, while hackney connects to the address it denotes. The same applies to a Location target when redirects are followed.

The IP-literal gate that hackney_url:normalize/2 applies to a percent-decoded host, added to close the percent-encoded IP bypass of CVE-2026-47076, passes the decoded value to inet_parse:address/1 as is. The connect path in hackney_happy:parse_address/1 drops a surrounding bracket pair, and the resolver ignores a trailing dot, so both forms pass the gate and still reach the literal address. Domain names with a trailing dot and unencoded IPv6 literals are not affected.

This issue affects hackney: from 4.0.1 before 4.9.0.

## Remediation

- workaround: Run the allowlist on the host that hackney_url:normalize/1 returns for the parsed URL, and strip a surrounding bracket pair and a trailing dot from it before the IP check, so the check sees the same address the connect path uses. (source: CNA: EEF)
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/benoitc/hackney/commit/f19561a0b422376348c91537e51377ab7325f4ee

## Affected products and versions

- benoitc / hackney (hackney): ≥ 4.0.1; < 4.9.0 (affected, semver). Source: CNA: EEF
- benoitc / hackney (benoitc/hackney): ≥ 452620a92ec1da2e6b4862a049a2a4f04b42068f; < f19561a0b422376348c91537e51377ab7325f4ee (affected, git). Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 6.9 (medium); CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N; source: CNA: EEF

- CVSS 4.0: 6.9 (medium); CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

- CISA KEV: No listing in collected sources

- EPSS: 0.14% as of 2026-11-02; percentile 3.15%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-436, CWE-918

## Exploit evidence

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

## References

- https://github.com/benoitc/hackney/releases/tag/4.9.0 (CNA: EEF; vendor-advisory, related)

- https://cna.erlef.org/cves/CVE-2026-115700.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-115700 (CNA: EEF; related)

- https://github.com/benoitc/hackney/pull/987 (CNA: EEF; related)

- https://github.com/benoitc/hackney/commit/452620a92ec1da2e6b4862a049a2a4f04b42068f (CNA: EEF; related)

- https://github.com/benoitc/hackney/commit/f19561a0b422376348c91537e51377ab7325f4ee (CNA: EEF; patch)

- https://cna.erlef.org/cves/CVE-2026-115700.html (6b3ad84c-e1a6-4bf7-a703-f496b71e49db)

- https://github.com/benoitc/hackney/commit/452620a92ec1da2e6b4862a049a2a4f04b42068f (6b3ad84c-e1a6-4bf7-a703-f496b71e49db)

- https://github.com/benoitc/hackney/commit/f19561a0b422376348c91537e51377ab7325f4ee (6b3ad84c-e1a6-4bf7-a703-f496b71e49db)

- https://github.com/benoitc/hackney/pull/987 (6b3ad84c-e1a6-4bf7-a703-f496b71e49db)

- https://github.com/benoitc/hackney/releases/tag/4.9.0 (6b3ad84c-e1a6-4bf7-a703-f496b71e49db)

- https://osv.dev/vulnerability/EEF-CVE-2026-115700 (6b3ad84c-e1a6-4bf7-a703-f496b71e49db)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-115700; retrieved 2026-11-02; source updated 2026-11-02

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-115700; retrieved 2026-11-03; source updated 2026-11-02

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-115700; retrieved 2026-11-02; source updated Not reported

Revision: 77184118c38d6ff256c878ff412a3c7fc84c9f7f3ab89fb057328b2b0dcca3a5

Canonical: https://y2.dev/cve/CVE-2026-115700

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