[CVE-2026-64577][MODERATE 7.0] gtp: check skb_pull_data() return in gtp1u_send_echo_resp() [ Upstream

[CVE-2026-64577][MODERATE 7.0] gtp: check skb_pull_data() return in gtp1u_send_echo_resp() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64577
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: gtp: check skb_pull_data() return in gtp1u_send_echo_resp() [ Upstream
Commit: b3c733eaae7f362601c28ac1533d47a961cd3e1c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3c733eaae7f362601c28ac1533d47a961cd3e1c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64577
Analysis date: Wed, 05 Aug 2026 05:17:45 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A remotely reachable GTP echo request with a short packet length can cause skb_pull_data() to fail silently, after which skb_push() may move skb data below skb head and trigger skb_under_panic(), causing a kernel crash.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64577 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64577

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 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64577	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-252;*CWE-20;CWE-754;Other CVSS 'AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '8.6';DESCR 'A remotely triggerable denial of service exists in the GTP echo response path because gtp1u_send_echo_resp() ignores a failed skb_pull_data() call. The receive path only guarantees 16 bytes, but the echo response code pulls 20 bytes, so a 16 to 19 byte GTP echo request can leave skb data unadvanced and then let skb_push() move the buffer pointer below skb head. This trips skb_under_panic() and can crash the kernel. For the CVSS the PR:N is used because an attacker only needs network reachability to the configured GTP UDP endpoint and does not need a local account on the target. The issue is network reachable when GTP support is enabled and exposed to untrusted peers. Impact is at least remote denial of service via kernel panic. For the paranoid score, limited confidentiality or integrity impact is kept only as a manual review sensitivity because the bug violates sk_buff bounds invariants, but the observed primitive is a checked underflow panic rather than a proven arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-64577 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DANGER NETWORK SKB KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. A short GTP echo request can be sent over the network to a configured GTP UDP endpoint.
* Reliable kernel crash / strong DoS: +1. The described path reaches skb_under_panic(), kernel BUG, and panic in interrupt context.
* Memory layout invariant restoration: +1. The patch restores the required skb data pointer invariant by checking skb_pull_data() before skb_push() and later tunnel header construction.
* No strong memory corruption primitive counted. The demonstrated behavior is a bounds invariant violation that is caught by skb_under_panic(), not a proven attacker-controlled overwrite.

Paranoid additional signal:

* Weak/indirect corruption candidate: +1. The bug moves skb->data below skb->head in a networking skb manipulation path, which is serious enough for manual review, but the visible primitive is still a checked underflow panic rather than arbitrary write, UAF, or type confusion.

Not counted:

* No local unprivileged trigger. The main trigger is remote packet delivery, not local code execution.
* No generic strong memory corruption +2. There is no demonstrated overwrite target, reclaim, UAF, double-free, or controlled payload corruption.
* No confidentiality or integrity score in the conservative ActionableScore. C:L/I:L is only a paranoid CVSS sensitivity, not a demonstrated primitive here.
* No broad/default exposure bonus. GTP is deployment-specific and normally requires configured GTP support.

## 3. Reachability analysis

A remote peer can trigger the bug if it can send a malformed 16 to 19 byte GTP echo request to a configured and reachable GTP endpoint. No local account on the target is required once the GTP UDP endpoint is exposed.

The path is not generally enabled on ordinary Linux hosts by default. It is relevant to systems using the kernel GTP driver, commonly in telecom, mobile core, packet gateway, or specialized tunneling deployments. Containers or namespaces mainly affect who can configure GTP devices, but the exploitation path itself is network-side after configuration.

Call-site confidence: high. The commit explicitly gives the caller, the guaranteed length mismatch, the failing skb_pull_data() behavior, the following skb_push(), and the observed panic trace.

## 4. Severity interpretation

This behaves more like an actionable Moderate remote DoS than an ordinary Moderate cleanup. The realistic demonstrated impact is a remote kernel panic against configured GTP deployments.

The theoretical concern is that skb pointer bounds invariants are violated in a network receive path, which justifies manual review and a paranoid score of 5. However, the patch does not show UAF, OOB write, object reuse, type confusion, callback control, or arbitrary memory corruption, so it should not be treated as a strong Important memory-corruption case solely from the patch.

## 5. One-sentence report phrase

A remotely reachable GTP echo request with a short packet length can cause skb_pull_data() to fail silently, after which skb_push() may move skb data below skb head and trigger skb_under_panic(), causing a kernel crash.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: the issue is network reachable in configured GTP deployments and affects sk_buff pointer bounds in a packet-processing path, even though the demonstrated impact is DoS rather than proven privilege escalation or arbitrary memory corruption.

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: gtp: check skb_pull_data() return in gtp1u_send_echo_resp() [ Upstream
Commit: b3c733eaae7f362601c28ac1533d47a961cd3e1c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b3c733eaae7f362601c28ac1533d47a961cd3e1c

Changed files:
  net/core/skbuff.c
  net/ipv4/ip_tunnel_core.c
  drivers/net/gtp.c
  net/ipv4/udp.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=b3c733eaae7f362601c28ac1533d47a961cd3e1c

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64577 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64577

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:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).