Created attachment 131960 [details]
Proof of concept

No validation of returned value leads to null dereference. The vulnerability is at 'Annot.cc:5404' in the function 'AnnotScreen::initialize'
Annot.cc
5403     action = LinkAction::parseAction(&obj1, doc->getCatalog()->getBaseURI());
5404     if (action->getKind() == actionRendition && page == 0) {
5405       error (errSyntaxError, -1, "Invalid Rendition action: associated screen annotation without P");
5406       delete action;
5407       action = NULL;
5408       ok = gFalse;
5409     }

In 5403 action gets a NULL value when it should be a LinkJavaScript object, however the getKind method is called in 5404 without checking if action is valid (!= NULL).

Prior to where the crash occurs, action is assigned a value:

5403        action = LinkAction::parseAction(&obj1, doc->getCatalog()->getBaseURI());

The line above calls the parseAction function with the object1 and a base URI that contains '0x7fffffffded0: "\020\337\377\377\377\177"' as baseURI which is not valid and so null is returned for action as shown below:

Link.cc
133   // action is missing or wrong type
134   } else {
135     error(errSyntaxWarning, -1, "parseAction: Unknown annotation action object: URI = '{0:s}'",
136           baseURI ? baseURI->getCString() : "NULL");
137     action = NULL;
138   }

This could be fixed just checking for action != NULL after Annot.cc:5403

PoC is attached.

This vulnerability has been found by Offensive Research at Salesforce.com:
Alberto Garcia (@algillera), Francisco Oca (@francisco_oca) & Suleman Ali (@Salbei_)