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Response snapshot Nov 4, 2026, 06:36 UTC

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VulnerabilityCVE-2026-10686

Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit.

Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. Both routing branches of ipv6_route_packet() (subsys/net/ip) were affected: the explicit-route path (net_route_packet()) and the on-link cross-interface path (net_route_packet_if()).

At a glance

Exploited
Not known
Severity
5.8 Medium (CVSS 3.1)
Chance of exploitation
0.5% in the next 30 days
Sources
2 independent sources

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-10686 (opens a new tab)

What happened

Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. Both routing branches of ipv6_route_packet() (subsys/net/ip) were affected: the explicit-route path (net_route_packet()) and the on-link cross-interface path (net_route_packet_if()). Each set the packet forwarding flag and called net_send_data() with the hop limit untouched and no expiry check.

Per RFC 8200 the hop-limit decrement is the mechanism that bounds packet lifetime and terminates routing loops; without it, a device acting as an IPv6 router relays looping packets indefinitely.

An on-path attacker who can induce or exploit a transient L3 loop turns it into a permanent forwarding storm, causing CPU/bandwidth resource exhaustion (availability DoS) on the forwarder and adjacent links; path-discovery and loop diagnostics that rely on hop-limit expiry are also defeated.

Affected configurations. In every affected release the forwarding path is reached via CONFIG_NET_ROUTE (enabled by default when CONFIG_NET_IPV6_NBR_CACHE is set), together with CONFIG_NET_ROUTING for cross-interface routing. Note that CONFIG_NET_IPV6_FORWARDING and CONFIG_NET_IPV4_FORWARDING — which appear in the fix and in this advisory's evidence notes — were introduced after v4.4.

Continue reading

0, when the routing options were split and renamed; they do not exist in any affected release. When auditing a v4.4.1-or-earlier configuration, look for CONFIG_NET_ROUTE and CONFIG_NET_ROUTING.

IPv4 is not affected in any release. The IPv4 forwarding path (net_route_ipv4_packet() in route_ipv4.c) was added after v4.4.0 and has never shipped in a release. Its TTL decrement and IPv4 header-checksum recomputation landed on main as part of the same fix, so the evidence notes below discuss it, but no released version is reachable by way of IPv4.

Affected releases are v1.8.0 through v4.4.1: v1.8.0 introduced net_route_packet() and v2.2.0 added net_route_packet_if(), and neither decremented the hop limit. v4.3.1 carries the explicit-route fix but not the on-link one, so it is affected as well. Fixed on main by 7d8f1afa7345 (explicit-route path) and 589eadc74efa (on-link path).

Scores and how they were measured

CVSS base severity

5.8

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.5%

Scored Percentile 43.9%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2026-10686 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    Vendor advisory (via NVD references) (opens a new tab)

    The vendor advisory referenced by the CVE record, for affected versions and fixes.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  4. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  5. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  6. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-10686, scored 2026-11-03. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 4). Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. (CVE-2026-10686). https://kevwire.com/record/CVE-2026-10686

MLA

"Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. (CVE-2026-10686)." KEVWire, 4 Nov. 2026, kevwire.com/record/CVE-2026-10686.

Chicago

KEVWire. "Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. (CVE-2026-10686)." Last modified November 4, 2026. https://kevwire.com/record/CVE-2026-10686.

Evidence summary (plain text)

Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. (Jul 31, 2026).
Zephyr's IPv6 forwarding path re-sent routed unicast packets without ever decrementing the IPv6 hop limit. Both routing branches of ipv6_route_packet() (subsys/net/ip) were affected: the explicit-route path (net_route_packet()) and the on-link cross-interface path (net_route_packet_if()). Each set the packet forwarding flag and called net_send_data() with the hop limit untouched and no expiry check.

Per RFC 8200 the hop-limit decrement is the mechanism that bounds packet lifetime and terminates routing loops; without it, a device acting as an IPv6 router relays looping packets indefinitely.
CVSS 5.8 (version 3.1; evidence as of Nov 4, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-10686).
EPSS 0.5% for the following 30 days, scored Nov 3, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-10686&date=2026-11-03).
Sources:
NVD CVE-2026-10686: https://nvd.nist.gov/vuln/detail/CVE-2026-10686
Vendor advisory (via NVD references): https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-4cg6-6jc4-2r6h
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-04T05:00:57.032Z&lastModEndDate=2026-11-04T06:35:55.811Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-04T04:31:09.055Z&lastModEndDate=2026-11-04T06:00:55.075Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-04T03:55:55.886Z&lastModEndDate=2026-11-04T05:30:57.785Z&resultsPerPage=500&startIndex=0
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-10686&date=2026-11-03
Record ID: CVE-2026-10686.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 4, 2026, 06:01 UTC. Ingestion is not an independent editorial investigation.

NVD status: Modified. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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