CVE-2025-39797
Full vulnerability record from the local CVENow database.
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.
Severity
HIGH
CVSS score
7.8
(v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-09-12 16:15:34.137000
Last modified
2026-10-30 13:18:09.707000
View original CVE JSON
{
"id": "CVE-2025-39797",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2025-09-12T16:15:34.137",
"lastModified": "2026-10-30T13:18:09.707",
"vulnStatus": "Modified",
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{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nxfrm: Duplicate SPI Handling\n\nThe issue originates when Strongswan initiates an XFRM_MSG_ALLOCSPI\nNetlink message, which triggers the kernel function xfrm_alloc_spi().\nThis function is expected to ensure uniqueness of the Security Parameter\nIndex (SPI) for inbound Security Associations (SAs). However, it can\nreturn success even when the requested SPI is already in use, leading\nto duplicate SPIs assigned to multiple inbound SAs, differentiated\nonly by their destination addresses.\n\nThis behavior causes inconsistencies during SPI lookups for inbound packets.\nSince the lookup may return an arbitrary SA among those with the same SPI,\npacket processing can fail, resulting in packet drops.\n\nAccording to RFC 4301 section 4.4.2 , for inbound processing a unicast SA\nis uniquely identified by the SPI and optionally protocol.\n\nReproducing the Issue Reliably:\nTo consistently reproduce the problem, restrict the available SPI range in\ncharon.conf : spi_min = 0x10000000 spi_max = 0x10000002\nThis limits the system to only 2 usable SPI values.\nNext, create more than 2 Child SA. each using unique pair of src/dst address.\nAs soon as the 3rd Child SA is initiated, it will be assigned a duplicate\nSPI, since the SPI pool is already exhausted.\nWith a narrow SPI range, the issue is consistently reproducible.\nWith a broader/default range, it becomes rare and unpredictable.\n\nCurrent implementation:\nxfrm_spi_hash() lookup function computes hash using daddr, proto, and family.\nSo if two SAs have the same SPI but different destination addresses, then\nthey will:\na. Hash into different buckets\nb. Be stored in different linked lists (byspi + h)\nc. Not be seen in the same hlist_for_each_entry_rcu() iteration.\nAs a result, the lookup will result in NULL and kernel allows that Duplicate SPI\n\nProposed Change:\nxfrm_state_lookup_spi_proto() does a truly global search - across all states,\nregardless of hash bucket and matches SPI and proto."
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nxfrm: Manejo de SPI Duplicado\n\nEl problema se origina cuando Strongswan inicia un mensaje Netlink XFRM_MSG_ALLOCSPI, lo que activa la función del kernel xfrm_alloc_spi(). Se espera que esta función garantice la unicidad del Índice de Parámetros de Seguridad (SPI) para las Asociaciones de Seguridad (SA) entrantes. Sin embargo, puede devolver éxito incluso cuando el SPI solicitado ya está en uso, lo que lleva a SPI duplicados asignados a múltiples SA entrantes, diferenciadas solo por sus direcciones de destino.\n\nEste comportamiento causa inconsistencias durante las búsquedas de SPI para paquetes entrantes. Dado que la búsqueda puede devolver una SA arbitraria entre aquellas con el mismo SPI, el procesamiento de paquetes puede fallar, lo que resulta en la pérdida de paquetes.\n\nSegún la sección 4.4.2 de RFC 4301, para el procesamiento entrante, una SA unicast se identifica de forma única por el SPI y, opcionalmente, el protocolo.\n\nReproducción Confiable del Problema:\nPara reproducir consistentemente el problema, restrinja el rango de SPI disponible en charon.conf: spi_min = 0x10000000 spi_max = 0x10000002\nEsto limita el sistema a solo 2 valores de SPI utilizables.\nA continuación, cree más de 2 SA secundarias (Child SA), cada una utilizando un par único de direcciones src/dst.\nTan pronto como se inicie la tercera SA secundaria (Child SA), se le asignará un SPI duplicado, ya que el grupo de SPI ya está agotado.\nCon un rango de SPI estrecho, el problema es consistentemente reproducible.\nCon un rango más amplio/predeterminado, se vuelve raro e impredecible.\n\nImplementación actual:\nLa función de búsqueda xfrm_spi_hash() calcula el hash usando daddr, proto y family.\nEntonces, si dos SA tienen el mismo SPI pero diferentes direcciones de destino, entonces:\na. Se dispersarán en diferentes cubos\nb. Se almacenarán en diferentes listas enlazadas (byspi + h)\nc. No se verán en la misma iteración de hlist_for_each_entry_rcu().\nComo resultado, la búsqueda dará como resultado NULL y el kernel permite ese SPI duplicado.\n\nCambio Propuesto:\nxfrm_state_lookup_spi_proto() realiza una búsqueda verdaderamente global, a través de todos los estados, independientemente del cubo de hash y coincide con el SPI y el protocolo."
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