CVE-2026-76470

Executive Summary

CVE-2026-76470 is a Cisco networking product vulnerability tracked under CWE-682 (Incorrect Calculation), rated CVSS 3.1 base score 8.8. According to the CNA description, it is one of multiple internally discovered issues addressed in a Cisco "software hardening release" resulting from an internal security review. The advisory provides no specific product line, affected version range, or resolvable patch identifier, so exploitation exposure cannot be confirmed from the supplied data alone; affected Cisco networking deployments should treat this as a high-severity, potentially remotely reachable flaw pending vendor clarification.

Technical Analysis

The only authoritative technical statement available is that the vulnerabilities tracked by CVE-2026-76470 relate to "incorrect calculation issues" grouped under the CWE Pillar CWE-682. CWE-682 is a pillar weakness — a parent category, not a leaf weakness — meaning the CNA has deliberately generalized the underlying root cause. Cisco's practice of publishing a single CVE for a batch of internally discovered issues means this identifier likely aggregates several distinct calculation defects rather than a single code path.

What can be stated factually:

Weakness class. CWE-682 ("Incorrect Calculation") covers arithmetic, conversion, rounding, scaling, truncation, and unit-handling defects. In networking software this class commonly manifests in buffer/length arithmetic, checksum or header-field computation, timer and expiry math, allocation-size derivation, and protocol field conversions. These are precisely the defect types that produce memory-safety consequences — most notably out-of-bounds writes or reads when a computed size is smaller or larger than the memory it is used against.

Impact chain implied by the CVSS vector. The vector CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H indicates:

• AV:A (Adjacent): exploitation is only viable from an adjacent network position — not AV:N. This is a meaningful constraint: the attacker must be on the same broadcast domain, an adjacent Layer 2/3 segment, or an otherwise adjacent network path (e.g., shared VLAN, peer link, or point-to-point adjacency).
• AC:L / PR:N / UI:N: no privileges required and no user interaction — the flaw is triggerable without credentials or victim action once network adjacency is achieved.
• C:H / I:H / A:H: high confidentiality, integrity, and availability impact when triggered — consistent with memory corruption enabling code execution, control-plane manipulation, or device crash/reboot.

Scope/attack surface. No function names, file paths, protocol identifiers, daemons, or management interfaces are named in the supplied description or title. The exact module — whether data plane, control plane, management plane, or a protocol handler — is not derivable from the data provided.

Assessment caveat. Because the CNA title is empty and the description is a generic hardening-release statement, no code-level root cause can be asserted. Any claim about a specific parser, protocol, or memory operation would be fabrication. The defensible technical characterization is: a set of incorrect-calculation defects in Cisco networking software, reachable from an adjacent network position without authentication, with high integrity/availability/confidentiality impact — the classic profile of a reachable computation flaw that leads to memory-safety corruption.

Exploitation Scenarios

No public proof-of-concept, exploit code, or Nuclei template exists for this CVE, and the advisory does not name the affected protocol, service, or component. The following chain is therefore described at the vulnerability-class level only; no specific functions, endpoints, parameters, or file paths are asserted because none are provided in the source data.

1) Reconnaissance / target identification. An adversary with or seeking adjacency to a Cisco network segment identifies candidate devices. In an adjacent-network–only attack (AV:A), the initial foothold is typically a compromised host, an unauthorized device, or a peer node placed on the same Layer 2 domain or adjacent routed segment. Target enumeration focuses on identifying Cisco device attributes (management/control interfaces reachable on the adjacent network, protocol version banners where exposed). This RECON step is generic and does not depend on the unknown details of the flaw.

2) Triggering the specific flaw class (incorrect calculation). Because the root cause is CWE-682, the trigger is a computation the vulnerable code performs on attacker-influenced or attacker-supplied values. At the class level, the adversary causes an arithmetic, length, or conversion computation to produce an incorrect result — e.g., an integer overflow, truncation, sign/unsigned error, or unit/scale mismatch — and then supplies or drives the surrounding data such that the flawed result is consumed by downstream logic (allocation, bounds check, buffer copy, or protocol decision). No privileges or user interaction are required per the CVSS vector (PR:N, UI:N), meaning the mis-computation and its consumption are reachable at the protocol/network level, not behind an authentication gate.

3) Payload / execution method (class level). With the calculation result malformed, the classical exploitation outcome is either (a) a memory-safety violation — an out-of-bounds write or read when the bad computed size is used to bound a memory operation — leading toward memory corruption, or (b) a logic-level integrity failure, where a protocol/algorithm decision based on the wrong value is accepted as valid. Because integrity and confidentiality impact are High, either misuse of data or corruption of device state is plausible. Exact bytes-in/bad-value-out mechanics cannot be specified without the vendor advisory details, and none are provided here.

4) Post-exploitation impact. Per the CVSS subscores, successful exploitation yields High confidentiality, integrity, and availability impact with unchanged scope (S:U). Practically: disclosure of sensitive data processed by the affected component (C:H), modification or corruption of device state/behavior (I:H), and denial of service — crash, reload, or service outage (A:H). On a networking device, availability impact on a control- or data-plane critical component can translate to segment-level or network-level outage. No evidence of in-the-wild exploitation, no public exploit, and no KEV listing exists in the supplied data; treat the chain above as a class-based inference, not a confirmed weaponized path.

Impact Assessment

• CVSS 3.1 base: 8.8 (High). Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
• Attack vector (AV:A, Adjacent): This is the primary mitigant. Exploitation requires an adjacent network position rather than arbitrary internet reachability. An attacker cannot simply hit the device from across the internet unless the vulnerable component is exposed to an adjacent network the attacker already shares or can reach.
• Complexity/low barrier (AC:L, PR:N, UI:N): Once adjacency exists, no race condition, no unusual conditions, no credentials, and no user interaction are required — lowering the effort needed after initial network placement.
• Confidentiality/Integrity/Availability all High: Loss of sensitive data, corruption of device behavior/data, and full denial of service are all within scope. On Cisco networking gear, High availability impact can mean device reload or a loss of forwarding, affecting everything downstream of the device.
• Scope unchanged (S:U): Impact is confined to the vulnerable component's security authority; the CVSS model does not expect cross-boundary escalation as part of the base scoring.
• Blast radius: Unknown precisely, because affected products and versions are not identified in the supplied data. Any organization running Cisco networking equipment with an attacker-reachable adjacent segment should assume potential applicability until the vendor advisory is reconciled to their inventory.
• Business impact: For network infrastructure, the combination of High A/I/C means potential service outage, traffic integrity compromise, and data exposure on a device that is typically trust-critical. Where the affected device is part of a network boundary or segmentation enforcement point, downstream exposure grows.
• Exploitation status: No PoC, no exploit code, no Nuclei template, no EPSS score (not yet scored by FIRST), and not listed in CISA KEV. Current likelihood of mass exploitation is not evidenced; severity is driven by the CVSS profile and the class of weakness, not by observed exploitation.

Detection Guidance

Because no specific protocol, port, method, or interface is named in the source data, the rule examples below target the vulnerability class (reachable incorrect-calculation / memory-corruption class against Cisco network devices) and rely on generic adjacent-network exploitation signals: device crash/reload correlation, malformed protocol traffic, and management-plane access anomalies. They detect suspicious conditions around the class of flaw, not a verified signature of this CVE. Tuning to actual Cisco advisory details is required before production use.

Sigma Rule

title: Cisco Networking Device — Crash or Reload Correlated with Adjacent-Network Traffic (CVE-2026-76470 class)
id: 3f9a1c2e-cve2-7647-0a11-b7c4a1e2d3f4
status: experimental
description: Detects Cisco device reload/crash or unexpected process restart events that may indicate exploitation of a reachable incorrect-calculation / memory-corruption vulnerability (CWE-682) triggered from an adjacent network position. Tune to vendor log source.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-76470
author: valtersit.com
date: 2026/01/01
logsource:
  product: cisco
  service: syslog
detection:
  selection_reload:
    message|contains:
      - 'SYS-2-RELOAD'
      - 'SYS-5-RELOAD'
      - 'SYS-6-RESTART'
      - 'unexpected restart'
      - 'Traceback'
      - 'Critical process'
  selection_adjacent:
    message|contains:
      - 'from '
      - 'adjacent'
  condition: selection_reload
falsepositives:
  - Planned maintenance reloads
  - Power events
  - Legitimate software upgrades
level: high

YARA Rule

rule CVE_2026_76470_CWE682_Hardening_Indicators
{
    meta:
        author = "valtersit.com"
        description = "Class-level indicators for CVE-2026-76470 (CWE-682 incorrect calculation in Cisco networking software). Detects firmware/software artifacts referencing the hardening release or calculation-defect hardening strings. Generic heuristic; tune to actual firmware images."
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76470"
        date = "2026-01-01"
        severity = "high"

    strings:
        $cve = "CVE-2026-76470" ascii wide nocase
        $cwe = "CWE-682" ascii wide nocase
        $reinforce1 = "hardening release" ascii wide nocase
        $reinforce2 = "incorrect calculation" ascii wide nocase
        $reinforce3 = "integer overflow" ascii wide nocase
        $reinforce4 = "out-of-bounds" ascii wide nocase
        $reinforce5 = "signedness" ascii wide nocase

    condition:
        ($cve or $cwe) or (2 of ($reinforce*))
}

Suricata IDS Rule

alert ip any any -> any any (msg:"CVE-2026-76470 Possible Cisco CWE-682 Memory-Corruption Probe (class-level, tune to protocol/port)"; flow:stateless; threshold: type both, track by_src, count 20, seconds 60; classtype:attempted-admin; reference:cve,2026-76470; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-76470; sid:2026764700; rev:1;)

Note: this rule is intentionally generic because the affected protocol and port are not provided in the source data. Replace ip any any -> any any and add protocol/port/content constraints once the Cisco advisory identifies the vulnerable component.

Elastic Detection

// Class-level: Cisco device restart/crash anomalies potentially linked to CVE-2026-76470 (CWE-682)
// Tune index and field names to the actual log pipeline.
sequence by host.id
  [ logs-cisco.syslog where event.action == "reload" or message : ("RELOAD", "unexpected restart", "Critical process") ]
  [ logs-cisco.syslog where message : ("Traceback", "assert", "out-of-bounds", "integer overflow", "signedness") ]
within 5m

Splunk SPL Query

index=network sourcetype=cisco:*
| eval cve_class = case(
    match(_raw, "(?i)RELOAD|unexpected restart|Critical process"), "reload_or_crash",
    match(_raw, "(?i)Traceback|assert|out-of-bounds|integer overflow|signedness"), "calc_or_memory_fault",
    1=1, "other")
| where cve_class != "other"
| stats count values(_raw) as evidence by host cve_class
| where count > 0
| sort - count

Wazuh OSSEC Rule

<group name="cisco,cve-2026-76470,">
  <rule id="100764" level="10">
    <decoded_as>cisco</decoded_as>
    <match>RELOAD|unexpected restart|Critical process|Traceback|out-of-bounds|integer overflow</match>
    <description>CVE-2026-76470 class: Cisco device crash/reload or calculation/memory fault; possible reachable CWE-682 exploitation from adjacent network</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Note: decoded_as and rule id must be reconciled with the deployed Wazuh decoder for Cisco logs; the match patterns target class-level indicators only.

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

• No vendor fix version, no workarounds, and no affected-version range are provided in the supplied data. The Cisco description references a "software hardening release," but no resolvable release identifier, advisory ID, or version string accompanies it. Treat the vulnerability as unpatched for planning purposes until the corresponding Cisco security advisory is located and mapped to your inventory.

1) Immediate mitigations

• Establish whether your Cisco networking devices are in scope by reconciling the (currently unspecified) affected product/version list from Cisco's official advisory with your asset inventory; the supplied data does not identify affected products.
• Constrain the adjacent attack vector: enforce network segmentation and 802.1X/NAC so an attacker cannot easily obtain adjacency to management and control-plane interfaces. AV:A is the primary exposure limiter — reducing who can reach the device at Layer 2/3 directly reduces risk.
• Apply management-plane access control: restrict reachability of device interfaces to trusted segments only, and monitor for unauthorized devices appearing on sensitive VLANs/segments.
• Enable and protect device logging (syslog to a remote, tamper-resistant collector) and alert on reloads, crashes, and unexpected process restarts that may indicate a DoS-triggering hit.
• Until a patch is confirmed, consider tightening protocol-level admission controls where configuration allows (e.g., filtering unnecessary protocol traffic from adjacent segments) to reduce reachable code paths.

2) Patch/upgrade steps

• Monitor Cisco's official security advisory portal for the advisory matching CVE-2026-76470 and obtain the exact fixed release for each affected product.
• Once the fixed release is published, plan a maintenance-window upgrade of all affected devices to the validated patched version; do not rely on the generic "hardening release" wording — verify the specific version.
• Validate post-upgrade with a device inventory sweep to confirm no affected versions remain.

3) Long-term hardening

• Maintain an authoritative, continuously updated inventory of Cisco firmware/software versions tuned to receive vendor advisory feeds.
• Standardize on worst-case CVSS remediation SLAs for network infrastructure given the High integrity/availability profile typical of this weakness class.
• Adopt rigorous fuzz-testing and static analysis for arithmetic/length/bounds math in custom or integrated code, addressing CWE-682 at the development stage.
• Deploy network anomaly detection for device crashes/reloads and correlate with adjacent-network traffic anomalies.
• Track CISA KEV and FIRST EPSS; note this CVE is not in KEV and is not yet scored by EPSS — reassess if either status changes.

References

• NVD — CVE-2026-76470: https://nvd.nist.gov/vuln/detail/CVE-2026-76470
• CWE-682: Incorrect Calculation (MITRE): https://cwe.mitre.org/data/definitions/682.html
• Cisco Security Advisories (vendor advisory portal; locate the advisory matching this CVE): https://sec.cloudapps.cisco.com/security/center/publicationListing.x
• CISA Known Exploited Vulnerabilities Catalog (CVE-2026-76470 not listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS (CVE-2026-76470 not yet scored): https://www.first.org/epss/
• MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/

No threat actor campaigns, exploit-in-the-wild evidence, public PoC, or KEV listing are associated with CVE-2026-76470 in the supplied data.