Description
pt_chown in the glibc package before 2.19-18+deb8u4 on Debian jessie; the elibc package before 2.15-0ubuntu10.14 on Ubuntu 12.04 LTS and before 2.19-0ubuntu6.8 on Ubuntu 14.04 LTS; and the glibc package before 2.21-0ubuntu4.2 on Ubuntu 15.10 and before 2.23-0ubuntu1 on Ubuntu 16.04 LTS and 16.10 lacks a namespace check associated with file-descriptor passing, which allows local users to capture keystrokes and spoof data, and possibly gain privileges, via pts read and write operations, related to debian/sysdeps/linux.mk. NOTE: this is not considered a vulnerability in the upstream GNU C Library because the upstream documentation has a clear security recommendation against the --enable-pt_chown option.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | glibc | 2.21-1 | — |
| Debian 13 | glibc | 2.21-1 | — |
| Debian 12 | glibc | 2.21-1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 14.04 LTS | eglibc | 2.19-0ubuntu6.8 | USN-2985-1 |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
Exploit-DB 1
- Ubuntu < 15.10 - PT Chown Arbitrary PTs Access Via User Namespace Privilege Escalation EDB-41760 · local · Feb 22, 2016
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Advisories 1
- USN-2985-1 eglibc, glibc vulnerabilities Ubuntu Security Notices (USN) · Apr 27, 2026
References
- http://www.halfdog.net/Security/2015/PtChownArbitraryPtsAccessViaUserNamespace/
- http://anonscm.debian.org/cgit/pkg-glibc/glibc.git/commit/?h=jessie&id=11475c083282c1582c4dd72eecfcb2b7d308c958
- [oss-security] 20160306 Re: Access to /dev/pts devices via pt_chown and user namespaces mailing-list
- 84601 vdb-entry
- USN-2985-2 vendor-advisory
- http://people.canonical.com/~ubuntu-security/cve/2016/CVE-2016-2856.html
- http://anonscm.debian.org/cgit/pkg-glibc/glibc.git/commit/?h=jessie&id=09f7764882a81e13e7b5d87d715412283a6ce403
- [oss-security] 20160223 Access to /dev/pts devices via pt_chown and user namespaces mailing-list
- USN-2985-1 vendor-advisory