Eclipse tinydtls before commit b3efd41ad111a4920f599f51ffa4f5e9f1e72221 contains an out-of-bounds read…

Eclipse tinydtls is a small-footprint DTLS implementation designed for constrained IoT devices — think CoAP endpoints, Zephyr/RIOT/Contiki sensors, the kind of node where mbedTLS or OpenSSL are too heavy. The flaw lives in check_server_certificate(), the client-side routine that validates an ECDSA certificate received during the DTLS handshake (ServerCertificate/ServerKeyExchange). A malformed cert message lets the parser walk past the end of the input buffer, producing a CWE-125 out-of-bounds read. All commits before b3efd41 are affected; the fix is in tip-of-trunk.

There is no vendor CVSS for this CVE — tinydtls is an Eclipse research-grade library and the advisory does not carry a scored vector. An out-of-bounds *read* in a handshake-time cert parser is genuinely on the low-to-moderate end: it's reachable pre-auth on the client side, but the realistic impact is a crash (DoS of one IoT device) or, on platforms with side-channel-readable memory, a small information leak. There is no documented path to RCE, no heap corruption, and the affected role — a sensor or CoAP client talking to a malicious DTLS server — is a narrow, low-value target. *LOW* is the honest assessment.

Why this verdict

• No write primitive: CWE-125 is read-only OOB. Without a corruption primitive, RCE chains require an additional bug that has not been published.
• Client-side trigger only: The attacker must lure the device into handshaking with malicious infrastructure. Most constrained IoT devices talk to one hardcoded backend over a controlled network path — exposure population is tiny.
• Dominant cipher-suite mode unaffected: tinydtls's flagship use case is PSK for sensor fleets; the vulnerable check_server_certificate() is only invoked in ECDHE-ECDSA / raw-public-key mode, which is a minority configuration.
• Role multiplier — low-value target: Affected role is a *constrained sensor / CoAP client*. Blast radius is a single device. Even on fleets, each handshake is independent — no lateral movement, no pivot.
• Role multiplier — no high-value role: tinydtls is explicitly *not* used in identity providers, hypervisors, PAM, CI/CD, backup, or kernel-mode agents. There is no canonical high-value deployment role to floor the verdict against.
• No KEV, no PoC, no campaigns: EPSS-class prior is <0.5%; nothing in the wild.

Why not higher?

MEDIUM/HIGH would require either a credible RCE chain (none published, and CWE-125 alone cannot produce one) or a high-value deployment role (tinydtls has none — it is a research-grade library for sensors). Network-reachable cert-parse bugs sound severe in OpenSSL or mbedTLS because of installed base; tinydtls's installed base is sensor firmware, not infrastructure.

Why not lower?

IGNORE is wrong because the bug *is* network-triggerable pre-auth, and a determined attacker on-path with a constrained-IoT client population could cause sustained DoS or harvest small memory fragments. SBOM-tracked firmware should still re-vendor at the next release cycle.

1. Inventory firmware SBOMs for tinydtls — Run syft or your firmware-SBOM tool against built images and grep for tinydtls / dtls.c checksum. This is hygiene — no mitigation SLA applies to a LOW verdict, so this can ride the standard 365-day remediation window.
2. Pin DTLS clients to PSK cipher suites where the use case allows — PSK mode (TLS_PSK_WITH_AES_128_CCM_8) does not invoke check_server_certificate() and is unaffected. If your fleet's threat model permits PSK, this eliminates exposure entirely. Apply during the next firmware revision.
3. Restrict outbound UDP/5684 from IoT VLANs to known backend IPs — Egress allowlisting on the CoAP/DTLS port denies the attacker the rogue-server scenario. Network-tier change, no firmware update required.
4. Re-vendor tinydtls at commit b3efd41 or later in the next firmware build — There is no tagged release. CI/build pipeline owners must bump the git pin and rebuild. noisgate remediation SLA for LOW is treat-as-backlog hygiene — fold into the next routine firmware cycle, not an emergency.

Run on a Linux build host or CI runner that has the firmware source tree checked out. Invoke as ./check-tinydtls.sh /path/to/firmware/src (no privileges required). The script grep-walks for vendored tinydtls and compares its dtls.c against the fix commit.

#!/usr/bin/env bash
# check-tinydtls.sh — detect Eclipse tinydtls pre-b3efd41 in a source tree
# Usage: ./check-tinydtls.sh <path-to-source-tree>
# Exit: 0 PATCHED, 1 VULNERABLE, 2 UNKNOWN/NOT FOUND
set -u

ROOT="${1:-.}"
FIX_COMMIT="b3efd41ad111a4920f599f51ffa4f5e9f1e72221"
FIX_SHORT="b3efd41"

if [[ ! -d "$ROOT" ]]; then
  echo "UNKNOWN: $ROOT is not a directory"
  exit 2
fi

# Find candidate tinydtls trees (dtls.c + dtls.h colocated)
mapfile -t HITS < <(find "$ROOT" -type f -name dtls.c 2>/dev/null | while read -r f; do
  d=$(dirname "$f")
  [[ -f "$d/dtls.h" && -f "$d/peer.c" ]] && echo "$d"
done)

if [[ ${#HITS[@]} -eq 0 ]]; then
  echo "UNKNOWN: no tinydtls source tree found under $ROOT"
  exit 2
fi

STATUS=0
for d in "${HITS[@]}"; do
  echo "[*] tinydtls candidate: $d"
  if [[ -d "$d/.git" || -f "$d/.git" ]]; then
    if git -C "$d" merge-base --is-ancestor "$FIX_COMMIT" HEAD 2>/dev/null; then
      echo "    PATCHED (fix $FIX_SHORT is ancestor of HEAD)"
    else
      echo "    VULNERABLE (fix $FIX_SHORT not in history)"
      STATUS=1
    fi
  else
    # No git metadata — fall back to source-level fingerprint of the fix
    if grep -qE 'check_server_certificate' "$d/dtls.c"; then
      # Heuristic: the post-fix code adds an explicit length-bound check before ECDSA parse
      if grep -qE 'data_length\s*<\s*sizeof.*ecdsa|bounds.*server.*cert' "$d/dtls.c"; then
        echo "    LIKELY PATCHED (bounds check present)"
      else
        echo "    LIKELY VULNERABLE (no post-fix bounds check fingerprint)"
        STATUS=1
      fi
    else
      echo "    UNKNOWN (check_server_certificate symbol missing — atypical fork)"
      [[ $STATUS -eq 0 ]] && STATUS=2
    fi
  fi
done

case $STATUS in
  0) echo "RESULT: PATCHED";;
  1) echo "RESULT: VULNERABLE";;
  2) echo "RESULT: UNKNOWN";;
esac
exit $STATUS

Sources

1. Eclipse Foundation — Known Vulnerabilities
2. Eclipse tinydtls — Gitiles repository (dtls.c)
3. cvedetails — Eclipse Tinydtls product page
4. cve.report — tinydtls
5. GitHub Advisory Database (unreviewed)
6. CWE-125: Out-of-bounds Read
7. MITRE CVE keyword search — out-of-bounds memory