SES prototype mostly working on latest Minefield, WebKit, and Chromium betas

Mark S. Miller erights at
Mon Aug 30 15:12:28 PDT 2010

May crash your browser or page:

<>Sources at

This has only been lightly tested and should **not** be relied on to have
any security properties yet.

The claim I working up to is that, on a securable ES5 implementation (<>), these scripts create
an SES environment (<>)
implementing the object-capability security model and solving the safe
mashup problem (<>).

Unfortunately, since there is not yet any full browser-based implementations
of ES5, the present state of these scripts have various compromises that
preserves their functionality but loses security. These are documented in
the various files under "KLUDGE SWITCHES". With these kludges, from
*extremely* light testing, it seems to work on the latest
* Firefox Minefield 4.0b5pre,
* Safari WebKit Nightly Version 5.0.1 (5533.17.8, r66356), and
* Chromium beta 6.0.490.0 (3135).
As soon as I get my VMWare installation fixed, I'll test on the IE9 preview
as well. Opera 10.61.8429 does not yet implement Object.getOwnPropertyNames,
so I can't even test there.

This implementation of SES cannot run on ES5/3 (<>)
as is because of the lack of a client side eval. The current plan is to
support SES5/3 directly, rather than porting these scripts to run on ES5/3.

Like ADsafe, this is all implemented by a lightweight client-side library,
with no server-side support need. Minified, the total size of the download
comes in under 5k. Because it does not parse or transform code, aside from
calls to "eval" or the "Function" constructor, the untrusted code runs at
full speed and with no code expansion. Due to various transient problems,
the safe eval is currently called "eval2" and "eval" remains unsafe.

Interestingly, this library contains a surprising faithful emulation of
WeakMaps on ES5 browsers that don't support WeakMaps directly (<

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