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CVE-2026-46300

net: skbuff: preserve shared-frag marker during coalescing

High Known exploited Linux
Severity
7.8 / 10
High · CVSS 3.1
Exploit chance (EPSS)
16.13%
Chance of exploitation in the next 30 days. Higher than 96.93% of scored vulnerabilities.
Known exploited
Yes
In CISA's catalog since Oct 28, 2026
Weakness
CWE-123 Write-what-where Condition
CWE-456 Missing Initialization of a Variable
CWE-787 Out-of-bounds Write
Fix
7.0.10
Upgrade Kernel to this version or later
Exploited in the wild. Linux Kernel Missing Initialization of a Variable Vulnerability (Linux Kernel). Required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. Due for U.S. federal agencies by Oct 31, 2026.

Description

In the Linux kernel, the following vulnerability has been resolved:

net: skbuff: preserve shared-frag marker during coalescing

skb_try_coalesce() can attach paged frags from @from to @to. If @from has SKBFL_SHARED_FRAG set, the resulting @to skb can contain the same externally-owned or page-cache-backed frags, but the shared-frag marker is currently lost.

That breaks the invariant relied on by later in-place writers. In particular, ESP input checks skb_has_shared_frag() before deciding whether an uncloned nonlinear skb can skip skb_cow_data(). If TCP receive coalescing has moved shared frags into an unmarked skb, ESP can see skb_has_shared_frag() as false and decrypt in place over page-cache backed frags.

Propagate SKBFL_SHARED_FRAG when skb_try_coalesce() transfers paged frags. The tailroom copy path does not need the marker because it copies bytes into @to's linear data rather than transferring frag descriptors.

Affected versions

Linux

PackageVulnerableFixed in
Kernel
>= 3.9.0, < 5.10.257
>= 5.11.0, < 5.15.208
>= 5.16.0, < 6.1.174
>= 6.2.0, < 6.6.141
>= 6.7.0, < 6.12.91
>= 6.13.0, < 6.18.33
>= 6.19.0, < 7.0.10
5.10.257
5.15.208
6.1.174
6.6.141
6.12.91
6.18.33
7.0.10

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

Kernel Linux → 7.0.10

Set Kernel to 7.0.10 or later in your manifest.

Severity breakdown

CVSS 3.1 7.8

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

Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Weakness

CWE-123: Write-what-where Condition

Any condition where the attacker has the ability to write an arbitrary value to an arbitrary location, often as the result of a buffer overflow.

How to prevent it
  • Architecture and Design: Use a language that provides appropriate memory abstractions.
  • Operation: Use OS-level preventative functionality integrated after the fact. Not a complete solution.

CWE-456: Missing Initialization of a Variable

The product does not initialize critical variables, which causes the execution environment to use unexpected values.

How to prevent it
  • Implementation: Ensure that critical variables are initialized before first use [REF-1485].
  • Requirements: Choose a language that is not susceptible to these issues.

CWE-787: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

How to prevent it
  • Requirements: Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
  • Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.
  • Operation, Build and Compilation: Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
  • Implementation: Consider adhering to the following rules when allocating and managing an application's memory: Double check that the buffer is as large as specified. When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string. Check buffer boundaries if accessing the buffer in a loop and make sure there is no danger of writing past the allocated space. If necessary, truncate all input strings to a reasonable length before passing them to the copy and concatenation functions.
  • Operation, Build and Compilation: Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code. Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking. For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
  • Operation: Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment. For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].
  • Implementation: Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.

References

Advisories

Issue reports

Packages

Other links

Timeline

  1. Published
  2. Added to CISA's Known Exploited Vulnerabilities catalog
  3. Last updated by the source
  4. Remediation due for U.S. federal agencies
  5. Latest EPSS score
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