# CVE-2026-121727: Kore before 4.3.0 Integer Underflow Memory Exhaustion via http_header_recv()

Status: published. Published: 2026-11-03. Updated: 2026-11-03.

Kore before 4.3.0 contains an integer underflow vulnerability in HTTP request body handling that allows unauthenticated attackers to bypass http_body_max by sending more body bytes than declared. Attackers can send oversized first segments over many concurrent POST, PUT or DELETE connections, wrapping content_length to grow buffers unbounded and exhaust worker memory.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/jorisvink/kore/commit/1ff3c0f6f7973dc7fc8bf38369790ef2d8079b3b

## Affected products and versions

- jorisvink / kore (jorisvink/kore): ≥ 0; < 4.3.0 (affected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 8.7 (high); 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; source: CNA: VulnCheck

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

- CVSS 4.0: 8.7 (high); 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/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: disclosure@vulncheck.com

- CVSS 3.1: 7.5 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-191

## Exploit evidence

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

## References

- https://github.com/jorisvink/kore/commit/1ff3c0f6f7973dc7fc8bf38369790ef2d8079b3b (CNA: VulnCheck; patch)

- https://github.com/jorisvink/kore (CNA: VulnCheck; product)

- https://kore.io/releases/4.3.0 (CNA: VulnCheck; release-notes)

- https://github.com/jorisvink/kore/blob/4.3.0-rc5/src/http.c#L934 (CNA: VulnCheck; technical-description)

- https://www.vulncheck.com/advisories/kore-before-4.3.0-integer-underflow-memory-exhaustion-via-http-header-recv (CNA: VulnCheck; third-party-advisory)

- https://github.com/jorisvink/kore (disclosure@vulncheck.com)

- https://github.com/jorisvink/kore/blob/4.3.0-rc5/src/http.c#L934 (disclosure@vulncheck.com)

- https://github.com/jorisvink/kore/commit/1ff3c0f6f7973dc7fc8bf38369790ef2d8079b3b (disclosure@vulncheck.com)

- https://kore.io/releases/4.3.0 (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/kore-before-4.3.0-integer-underflow-memory-exhaustion-via-http-header-recv (disclosure@vulncheck.com)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-121727; retrieved 2026-11-03; source updated 2026-11-03

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-121727; retrieved 2026-11-04; source updated 2026-11-03

Revision: 70be94c2d957d78caed64fa04b6b2ae57c86f4908539c2cce3362b63e9749148

Canonical: https://y2.dev/cve/CVE-2026-121727

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