* [CVE-2026-98850][MODERATE REGULAR] net/packet: prevent TX_RING byte count overflow
@ 2026-10-24 17:04 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-24 17:04 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98850
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/packet: prevent TX_RING byte count overflow
Commit: be12b221c0301111eeb023be04add3c6ad7c21fe
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=be12b221c0301111eeb023be04add3c6ad7c21fe
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98850
Analysis date: Sat, 24 Oct 2026 13:04:10 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A CAP_NET_RAW holder can recycle AF_PACKET TX_RING frames until the signed send-byte count wraps negative and triggers a kernel BUG, with possible host panic under panic-on-oops.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98850 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98850
The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.
The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.
Published priority for this report: MODERATE REGULAR
Manual review required: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98850 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98850 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-190;CWE-617;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A signed integer overflow in tpacket_snd can occur because a blocking AF_PACKET TX_RING send accumulates transmitted byte counts in an int while another userspace thread recycles completed frames. After more than INT_MAX bytes the result can become a negative internal errno such as -EIOCBQUEUED, causing sock_sendmsg_nosec to reach a BUG condition. For the CVSS the PR:L value is selected because reliable triggering requires local code execution and CAP_NET_RAW, but this capability may be delegated to containers or obtained in permitted user and network namespaces. The demonstrated primitive is a reachable kernel BUG rather than memory corruption. Confidentiality and integrity remain unaffected. Availability is low in the base case because an oops does not always stop the host, while systems using panic_on_oops can suffer a host wide kernel panic. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to MODERATE because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were V30_AEGIS_DISTANCE_REVIEW_MODERATE and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 6.5 and ActionableScore 2 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE REMOTE READ LOCK DANGER SIMPLEFIX SKB PACKET V30_AEGIS_DISTANCE_REVIEW_MODERATE V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 0.
* Conservative score: 0.
* Raw paranoid score: 0.
* Paranoid score: 0.
* No floor or cap applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable kernel crash/strong DoS: accumulated `len_sum` wraps to a negative internal errno, causing `sock_sendmsg_nosec()` to reach `BUG`; host panic is possible with `panic_on_oops`.
* -1 Reduced privilege requirement: the demonstrated trigger requires `CAP_NET_RAW`, which is below full host-administrator power but is still a privileged capability.
* No memory-corruption point: the patch prevents signed byte-count overflow; it does not show an OOB access, UAF, stale pointer, or write outside an allocation.
* No additional availability point: oops and configured panic are the same terminal failure path.
* No C/I, arbitrary-write, authorization-bypass, or privilege-escalation signal.
* B5-R does not apply: there is retry/recycling accumulation, but no heap/slab OOB write or subsequent consumption of corrupted structured state.
* B3-PENDING and B4-PENDING do not apply.
3. Reachability analysis
A local `CAP_NET_RAW` holder can set up an AF_PACKET `TPACKET_V2` TX ring and use concurrent frame recycling to keep one blocking send draining frames beyond the ring’s nominal size. No host UID 0 requirement is shown. CAP_NET_RAW may be delegated or obtainable in permitted user/network namespaces, but the evidence does not establish that the complete trigger is namespace-obtainable on every assessed system; therefore namespace scope remains unknown. No special hardware or timing race is required, though substantial repeated transmission is needed.
4. Primitive and severity reading
The primitive is a signed integer overflow in a return-byte accumulator, followed by semantic collision with a negative errno and a kernel `BUG`. This is CLASS_C crash/DoS behavior, not heap corruption. The shown effect is an oops and, under `panic_on_oops`, possible host-wide panic. No useful non-crash primitive remains after excluding that failure. Consequently it is not an Important candidate and may be downgraded through normal Moderate handling after review.
5. One-sentence report phrase
A CAP_NET_RAW holder can recycle AF_PACKET TX_RING frames until the signed send-byte count wraps negative and triggers a kernel BUG, with possible host panic under panic-on-oops.
6. Manual review advice
MANUAL CHECK RECOMMENDED
Confirm product user-namespace policy, CAP_NET_RAW delegation, and panic-on-oops configuration.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: net/packet: prevent TX_RING byte count overflow
Commit: be12b221c0301111eeb023be04add3c6ad7c21fe
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=be12b221c0301111eeb023be04add3c6ad7c21fe
Commit description:
tpacket_snd() drains every SEND_REQUEST frame in a TX ring and adds
each valid packet length to the signed int len_sum. Userspace can
recycle completed frames concurrently, so a single blocking send call
is not bounded by the ring size.
After enough successful transmissions len_sum wraps into the negative
range. In particular, 65536 65535-byte frames followed by a 65007-byte
frame produce 0xfffffdef, or -EIOCBQUEUED. sock_sendmsg_nosec() treats
that as an impossible return and triggers a BUG. On systems configured
to panic on oops, a CAP_NET_RAW holder can panic the host kernel.
Stop before the next frame would make the byte count exceed INT_MAX.
The positive short count leaves that frame pending for a later send
call.
A two-thread TPACKET_V2 reproducer triggered the BUG on an arm64 build
of Linux 7.3-rc4. With this change, the same reproducer returned the
expected positive short count without an oops.
Fixes: 69e3c75 ("net: TX_RING and packet mmap")
Cc: [email protected]
Signed-off-by: Ilkka Lappeteläinen <[email protected]>
Reviewed-by: Willem de Bruijn <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
net/packet/af_packet.c
Diff excerpt:
Not included in this email. See the upstream URL for the full patch.
Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=be12b221c0301111eeb023be04add3c6ad7c21fe
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98850 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98850
The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.
The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.
This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.
The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.
Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:
Conservative CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.
CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.
A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.
Conservative ActionableScore: unknown
Paranoid ActionableScore: 0
The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.
For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:
ActionableScore below 5 -> MODERATE REGULAR
ActionableScore 5 or more -> MODERATE 7.0
The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.
There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).
KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.
AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR
These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).
Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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