UBUNTU-CVE-2025-38067
In the Linux kernel, the following vulnerability has been resolved: rseq: Fix segfault on registration when rseq_cs is non-zero The rseq_cs field is documented as being set to 0 by user-space prior to registration, however this is not currently enforced by the kernel. This can result in a segfault on return to user-space if the value stored in the rseq_cs field doesn't point to a valid struct rseq_cs. The correct solution to this would be to fail the rseq registration when the rseq_cs field is non-zero. However, some older versions of glibc will reuse the rseq area of previous threads without clearing the rseq_cs field and will also terminate the process if the rseq registration fails in a secondary thread. This wasn't caught in testing because in this case the leftover rseq_cs does point to a valid struct rseq_cs. What we can do is clear the rseq_cs field on registration when it's non-zero which will prevent segfaults on registration and won't break the glibc versions that reuse rseq areas on thread creation.
02 / AFFECTED SOFTWARE
Affected packages
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03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: rseq: Fix segfault on registration when rseq_cs is non-zero The rseq_cs field is documented as being set to 0 by user-space prior to registration, however this is not currently enforced by the kernel. This can result in a segfault on return to user-space if the value stored in the rseq_cs field doesn't point to a valid struct rseq_cs. The correct solution to this would be to fail the rseq registration when the rseq_cs field is non-zero. However, some older versions of glibc will reuse the rseq area of previous threads without clearing the rseq_cs field and will also terminate the process if the rseq registration fails in a secondary thread. This wasn't caught in testing because in this case the leftover rseq_cs does point to a valid struct rseq_cs. What we can do is clear the rseq_cs field on registration when it's non-zero which will prevent segfaults on registration and won't break the glibc versions that reuse rseq areas on thread creation.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/fd881d0a085fc54354414aed990ccf05f282ba53
- https://git.kernel.org/stable/c/2df285dab00fa03a3ef939b6cb0d0d0aeb0791db
- https://git.kernel.org/stable/c/fd881d0a085fc54354414aed990ccf05f282ba53
- https://ubuntu.com/security/CVE-2025-38067
- https://ubuntu.com/security/notices/USN-7769-1
- https://ubuntu.com/security/notices/USN-7769-2
- https://ubuntu.com/security/notices/USN-7769-3
- https://ubuntu.com/security/notices/USN-7770-1
- https://ubuntu.com/security/notices/USN-7771-1
- https://ubuntu.com/security/notices/USN-7774-1
- https://ubuntu.com/security/notices/USN-7774-2
- https://ubuntu.com/security/notices/USN-7774-3
- https://ubuntu.com/security/notices/USN-7774-4
- https://ubuntu.com/security/notices/USN-7774-5
- https://ubuntu.com/security/notices/USN-7775-1
- https://ubuntu.com/security/notices/USN-7775-2
- https://ubuntu.com/security/notices/USN-7775-3
- https://ubuntu.com/security/notices/USN-7776-1
- https://ubuntu.com/security/notices/USN-7789-1
- https://ubuntu.com/security/notices/USN-7789-2
- https://ubuntu.com/security/notices/USN-8028-1
- https://ubuntu.com/security/notices/USN-8028-2
- https://ubuntu.com/security/notices/USN-8028-3
- https://ubuntu.com/security/notices/USN-8028-4
- https://ubuntu.com/security/notices/USN-8028-5
- https://ubuntu.com/security/notices/USN-8028-6
- https://ubuntu.com/security/notices/USN-8028-7
- https://ubuntu.com/security/notices/USN-8028-8
- https://ubuntu.com/security/notices/USN-8031-1
- https://ubuntu.com/security/notices/USN-8031-2
- https://ubuntu.com/security/notices/USN-8031-3
- https://ubuntu.com/security/notices/USN-8052-1
- https://ubuntu.com/security/notices/USN-8052-2
- https://ubuntu.com/security/notices/USN-8074-1
- https://ubuntu.com/security/notices/USN-8074-2
- https://ubuntu.com/security/notices/USN-8126-1
- https://www.cve.org/CVERecord?id=CVE-2025-38067