# CVE-2025-39797: xfrm: Duplicate SPI Handling

> A flaw in Linux kernel IPsec handling allows duplicate Security Parameter Indexes, causing packet drops and denial of service when specific configurations are used.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Sep 2025
- **Updated:** 11 May 2026
- **Also known as:** AZL-67334, AZL-70760, BELL-CVE-2025-39797, DEBIAN-CVE-2025-39797, GHSA-p94f-8hph-rvrp, ROOT-OS-DEBIAN-11-CVE-2025-39797, ROOT-OS-DEBIAN-12-CVE-2025-39797, ROOT-OS-UBUNTU-2204-CVE-2025-39797, ROOT-OS-UBUNTU-2404-CVE-2025-39797, UBUNTU-CVE-2025-39797

## What is CVE-2025-39797?

CVE-2025-39797 is a high-severity denial of service vulnerability in Linux kernel, published on 12 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

## Which versions are affected by CVE-2025-39797?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39797?

Apply the vendor's patch.

## Is CVE-2025-39797 being exploited?

There is no known exploitation of CVE-2025-39797 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39797 and fix it if it is affected.

What it is: CVE-2025-39797 is a high-severity denial of service vulnerability in Linux kernel, published on 12 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-39797 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-39797/ (Markdown: https://insights.sbomify.com/CVE-2025-39797/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39797
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39797
- OSV: https://osv.dev/vulnerability/CVE-2025-39797

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39797/
Summaries are generated and may contain mistakes; the official description above is the record.