linux-cve-announce - CVE-2025-39797: xfrm: Duplicate SPI Handling

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Message-ID: <2025091224-CVE-2025-39797-b0f7@gregkh>
Date: Fri, 12 Sep 2025 17:59:27 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39797: xfrm: Duplicate SPI Handling

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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

xfrm: Duplicate SPI Handling

The issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI
Netlink message, which triggers the kernel function xfrm_alloc_spi().
This function is expected to ensure uniqueness of the Security Parameter
Index (SPI) for inbound Security Associations (SAs). However, it can
return success even when the requested SPI is already in use, leading
to duplicate SPIs assigned to multiple inbound SAs, differentiated
only by their destination addresses.

This behavior causes inconsistencies during SPI lookups for inbound packets.
Since the lookup may return an arbitrary SA among those with the same SPI,
packet processing can fail, resulting in packet drops.

According to RFC 4301 section 4.4.2 , for inbound processing a unicast SA
is uniquely identified by the SPI and optionally protocol.

Reproducing the Issue Reliably:
To consistently reproduce the problem, restrict the available SPI range in
charon.conf : spi_min = 0x10000000 spi_max = 0x10000002
This limits the system to only 2 usable SPI values.
Next, create more than 2 Child SA. each using unique pair of src/dst address.
As soon as the 3rd Child SA is initiated, it will be assigned a duplicate
SPI, since the SPI pool is already exhausted.
With a narrow SPI range, the issue is consistently reproducible.
With a broader/default range, it becomes rare and unpredictable.

Current implementation:
xfrm_spi_hash() lookup function computes hash using daddr, proto, and family.
So if two SAs have the same SPI but different destination addresses, then
they will:
a. Hash into different buckets
b. Be stored in different linked lists (byspi + h)
c. Not be seen in the same hlist_for_each_entry_rcu() iteration.
As a result, the lookup will result in NULL and kernel allows that Duplicate SPI

Proposed Change:
xfrm_state_lookup_spi_proto() does a truly global search - across all states,
regardless of hash bucket and matches SPI and proto.

The Linux kernel CVE team has assigned CVE-2025-39797 to this issue.

Affected and fixed versions
===========================

	Fixed in 6.6.103 with commit 3d8090bb53424432fa788fe9a49e8ceca74f0544
	Fixed in 6.12.43 with commit 2fc5b54368a1bf1d2d74b4d3b8eea5309a653e38
	Fixed in 6.15.11 with commit c67d4e7a8f90fb6361ca89d4d5c9a28f4e935e47
	Fixed in 6.16.2 with commit 29e9158f91f99057dbd35db5e8674d93b38549fe
	Fixed in 6.17-rc1 with commit 94f39804d891cffe4ce17737d295f3b195bc7299

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-39797
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/xfrm/xfrm_state.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3d8090bb53424432fa788fe9a49e8ceca74f0544
	https://git.kernel.org/stable/c/2fc5b54368a1bf1d2d74b4d3b8eea5309a653e38
	https://git.kernel.org/stable/c/c67d4e7a8f90fb6361ca89d4d5c9a28f4e935e47
	https://git.kernel.org/stable/c/29e9158f91f99057dbd35db5e8674d93b38549fe
	https://git.kernel.org/stable/c/94f39804d891cffe4ce17737d295f3b195bc7299