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Zsh Multiple Denial of Service Vulnerabilities

Low

Synopsis

Tenable has found multiple Denial of Service vulnerabilities affecting the Zsh runtime. The root cause for the following crashes are all out-of-bounds memory reads:

taddrstr function in text.c

Using "!" without following command could result in a crash within taddrstr function.

bin_print function in builtin.c

An out-of-range argument specifier used in printf could result in a crash within bin_print function.

getjobs function in jobs.c

Integer overflow in job number could result in a crash within getjobs function.

hasher function in hashtable.c

Using "typeset" with -T and -p arguments together could result in a crash within hasher function.

Solution

Update to latest Zsh version found git://git.code.sf.net/p/zsh/code

Disclosure Timeline

05/10/2019 - Initial disclosure to zsh-workers.
05/10/2019 - Zsh-workers asks how this could be exploited.
05/10/2019 - Zsh-worker does initial bug assessment, confirms crashes.
05/12/2019 - Zsh-workers explain "protected mode" could be a possible attack scenario and suggests better warnings displayed for users using restricted mode.
05/13/2019 - Tenable emphasizes the crashes root cause are invalid memory access, which could potential be abused for an infoleak step in exploitation process. Asks for patch release expectations.
05/13/2019 - Zsh-workers inform that someone is looking into fixing the crashes, but no expected patch date.
05/22/2019 - Zsh-worker says they have patched the issues and ask for confirmation. Also inform that exploitation of bugs is unlikely.
05/30/2019 - Tenable confirms issues are patched.

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

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