CVE-2026-6679 - wolfSSL DTLS 1.3 ACK serialization heap overflow

CVE-2026-6679 + wolfSSL DTLS 1.3 ACK serialization heap overflow + High + 2026-06-25

One-sentence business risk

Unauthenticated DTLS peers can corrupt memory before trust is established, making exposed DTLS services a production crash or code-execution risk.

Research notes

  • Root cause: A heap buffer overflow could occur in the DTLS 1.3 ACK serialization path before the connecting peer is authenticated.
  • Affected versions: wolfSSL 5.4.0 through 5.9.0 builds using DTLS 1.3.
  • Fixed / safe versions: wolfSSL 5.9.1 or later.
  • Public exploit / PoC signal: public PoC or exploit details are referenced by NVD; use only safe regression tests and do not execute exploit payloads against production.
  • CVSS: 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Exact vulnerable code pattern

uint32_t count = read_u32(peer);
attrs = calloc(count, sizeof(*attrs));
for (i = 0; i < count; i++) attrs[i] = parse_attr(peer);

Fixed / mitigated code pattern

uint32_t count = read_u32(peer);
if (count > MAX_ATTRS || count > SIZE_MAX / sizeof(*attrs)) return PROTOCOL_ERROR;
attrs = calloc(count, sizeof(*attrs));
for (i = 0; i < count; i++) parse_attr_checked(peer, &attrs[i]);

Dependency or runtime update:

rg -n "wolfSSL|DTLS|X509|ALPN|SNI" .
# update wolfSSL package/submodule to wolfSSL 5.9.1 or later
ctest --output-on-failure

Step-by-step integration guide

  1. Inventory wolfSSL in source, lockfiles, SBOMs, CI images, containers, deployment manifests, and managed runtimes.
  2. Upgrade or patch to wolfSSL 5.9.1 or later; if no upstream package is available, apply the local guard shown above and track the vendor release as a blocking follow-up.
  3. Replace every vulnerable memory-safety pattern with a fail-closed implementation that validates ownership, bounds, canonical paths, origin/session binding, or parser limits before acting.
  4. Add a regression test that reproduces the advisory shape safely and proves the request is rejected, bounded, or authorized.
  5. Deploy through canary, monitor auth, file, parser, crash, and CI-runner logs, then remove temporary edge blocks only after all runtimes are fixed.

Alternative mitigations

  • Disable the vulnerable feature path, decoder, plugin, runner backend, proxy agent, or route while the patch rolls out.
  • Add WAF/reverse-proxy rules for SQL metacharacters, traversal tokens, unsafe Docker flags, oversized/nested payloads, or unexpected session-origin transitions matching this trigger class.
  • Restrict egress and access to untrusted artifacts, SSH servers, media uploads, workflow execution, and administrative delegation until fixed versions are verified.
  • Rotate credentials and invalidate sessions if logs show the vulnerable path was reachable by untrusted users.

Detection signature

id: cve-2026-6679-wolfssl-dtls-1-3-ack-serialization-heap-overflow
source: NVD
package_or_product: "wolfSSL"
affected: "wolfSSL 5.4.0 through 5.9.0 builds using DTLS 1.3"
fixed: "wolfSSL 5.9.1 or later"
cvss: "7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
signals:
  - "memory-safety"
  - "CVE-2026-6679"
  - "wolfSSL"
action: "upgrade, add a regression test, and verify deploy artifact"

Copy-paste skill

You are remediating CVE-2026-6679 (wolfSSL DTLS 1.3 ACK serialization heap overflow) in this repository.

Produce a reviewer-ready PR or TRIAGE.md. Inventory wolfSSL across source, lockfiles, images, CI, deployment manifests, and SBOMs. Apply wolfSSL 5.9.1 or later. Replace the vulnerable memory-safety pattern with the fail-closed pattern, add a regression test for the advisory trigger, and document owner, rollout, rollback, and validation evidence. Do not run public exploit PoCs against production or expose secrets in logs.

Keywords, affected tech stack, and revenue tags

  • Keywords: CVE-2026-6679, memory-safety, wolfSSL, NVD.
  • Affected tech stack: c/c++.
  • Revenue tags: sellable_to_fintech, enterprise_blocker, high_priority_sla.

References