CVE-2026-64531

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

net: openvswitch: reject oversized nested action attrs

Open vSwitch stores generated flow actions as nlattrs, whose nla_len field is u16. Commit a1e64addf3ff (net: openvswitch: remove misbehaving actions length check) allowed the total sw_flow_actions stream to grow beyond 64 KiB, which is valid, but also removed the last guard preventing a generated nested action attribute from exceeding U16_MAX.

An oversized generated container can thus be closed with a truncated nla_len. A later dump or teardown then walks a structurally different stream than the one that was validated. In particular, an oversized nested CLONE/CT action may cause subsequent bytes in the generated stream to be interpreted as independent actions.

Keep the larger total-action-stream behavior, but make nested action close reject generated containers that do not fit in nla_len, and return the error through all callers. For recursive SAMPLE, CLONE, DEC_TTL, and CHECK_PKT_LEN builders, trim resource-owning action-list tails in reverse construction order before discarding failed wrappers, so resources copied into the rejected tails are released before the wrappers are removed.

Most failed outer wrappers are discarded by truncating actions_len after child resources have been released. CHECK_PKT_LEN also trims its parent after branch resources are gone. SET/TUNNEL close failures unwind their known tun_dst ownership directly, and SET_TO_MASKED has no external ownership and truncates on close failure.

Weakness

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• If possible, choose a language or compiler that performs automatic bounds checking.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
• Use libraries or frameworks that make it easier to handle numbers without unexpected consequences.
• Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]
• Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
• Use unsigned integers where possible. This makes it easier to perform validation for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.
• Understand the programming language’s underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, “not-a-number” calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7]
• Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/92.html

References

• https://git.kernel.org/stable/c/1b41cbe05b184f8861712f0806cc0c4f5d8c6dfe
• https://git.kernel.org/stable/c/3f1f755366687d051174739fb99f7d560202f60b
• https://git.kernel.org/stable/c/ab855641241387db062a5e41d9ad6b8561542572
• https://git.kernel.org/stable/c/c66bd2626c2764f23764ff0f8277f44a9cfe8349
• https://git.kernel.org/stable/c/d573250d228401f707f4dbc09d11227a6215ee5f
• https://git.kernel.org/stable/c/dbd14f736be02cfe73049bd801af89becd1a0749
• https://git.kernel.org/stable/c/f1efff8858403191361a01269c6fe8dd7f55a385
• http://www.openwall.com/lists/oss-security/2026/07/28/8
• http://www.openwall.com/lists/oss-security/2026/07/31/17
• http://www.openwall.com/lists/oss-security/2026/08/01/1
• http://www.openwall.com/lists/oss-security/2026/08/01/3
• http://www.openwall.com/lists/oss-security/2026/08/22/1