'"Virtually all compilers -- programs that transform human-readable source code into computer-executable machine code -- are vulnerable to an insidious attack in which an adversary can introduce targeted vulnerabilities into any software without being detected," warns cybersecurity expert Brian Krebs in a new report. An anonymous reader shares an excerpt: Researchers with the University of Cambridge discovered a bug that affects most computer code compilers and many software development environments. At issue is a component of the digital text encoding standard Unicode, which allows computers to exchange information regardless of the language used. Unicode currently defines more than 143,000 characters across 154 different language scripts (in addition to many non-script character sets, such as emojis). Specifically, the weakness involves Unicode's bi-directional or "Bidi" algorithm, which handles displaying text that includes mixed scripts with different display orders, such as Arabic -- which is read right to left -- and English (left to right). But computer systems need to have a deterministic way of resolving conflicting directionality in text. Enter the "Bidi override," which can be used to make left-to-right text read right-to-left, and vice versa. "In some scenarios, the default ordering set by the Bidi Algorithm may not be sufficient," the Cambridge researchers wrote. "For these cases, Bidi override control characters enable switching the display ordering of groups of characters." Bidi overrides enable even single-script characters to be displayed in an order different from their logical encoding. As the researchers point out, this fact has previously been exploited to disguise the file extensions of malware disseminated via email. Here's the problem: Most programming languages let you put these Bidi overrides in comments and strings. This is bad because most programming languages allow comments within which all text -- including control characters -- is ignored by compilers and interpreters. Also, it's bad because most programming languages allow string literals that may contain arbitrary characters, including control characters. "So you can use them in source code that appears innocuous to a human reviewer [that] can actually do something nasty," said Ross Anderson, a professor of computer security at Cambridge and co-author of the research. "That's bad news for projects like Linux and Webkit that accept contributions from random people, subject them to manual review, then incorporate them into critical code. This vulnerability is, as far as I know, the first one to affect almost everything." The research paper, which dubbed the vulnerability "Trojan Source," notes that while both comments and strings will have syntax-specific semantics indicating their start and end, these bounds are not respected by Bidi overrides. [...] Anderson said such an attack could be challenging for a human code reviewer to detect, as the rendered source code looks perfectly acceptable. "If the change in logic is subtle enough to go undetected in subsequent testing, an adversary could introduce targeted vulnerabilities without being detected," he said. Equally concerning is that Bidi override characters persist through the copy-and-paste functions on most modern browsers, editors, and operating systems.' -- source: https://it.slashdot.org/story/21/11/01/2147254 Cheers, Peter -- Peter Reutemann Dept. of Computer Science University of Waikato, NZ +64 (7) 858-5174 (office) +64 (7) 577-5304 (home office) http://www.cms.waikato.ac.nz/~fracpete/ http://www.data-mining.co.nz/