This topic came up as a sub-point to another question a few weeks ago, I ended up doing a fair bit of research with not much in terms of concrete results. I'll start with the USA since they're basically the only major copyright jurisdiction for which I could find a straightforward answer, then discuss internationally.
In the USA, Bob would generally not hold copyright in modifications thus there is no copyright for Alice to violate, assuming no copyright exceptions like fair use apply. This is due to 17 U.S.C 103(a) (see also Anderson v. Stallone):
The subject matter of copyright as specified by section 102 includes compilations and derivative works, but protection for a work employing preexisting material in which copyright subsists does not extend to any part of the work in which such material has been used unlawfully.
While I couldn't find any commentary on this point, the wording does seem to imply that portions of a derivative with additions far enough removed from the original work might qualify for copyright protection.
International copyright law
The main provisions governing derivative works in international copyright law come from Berne Convention Article 2(3):
Translations, adaptations, arrangements of music and other alterations of a literary or artistic work shall be protected as original works without prejudice to the copyright in the original work.
and Article 12 (with a similar provision specifically for translation in Article 8):
Authors of literary or artistic works shall enjoy the exclusive right of authorizing adaptations, arrangements and other alterations of their works.
There's the argument that since unauthorized derivatives aren't explicitly excluded from protection that they should be protected, however, there's also the argument that granting unauthorized derivatives their own copyright is in itself prejudicial to the original copyright holder. Note I don't think it's debated that non-infringing derivatives gain their own copyright, including unauthorized derivatives that nevertheless fall into a copyright exception such as fair use.
Dr. Daniel Gervais points out in The Derivative Right, or Why Copyright Law Protects Foxes Better than Hedgehogs section III.B that there's a bit of history here. The original Berne Convention 1886 text stated that "Lawful translations shall be protected as original works." However, the word "lawful" was struck out in the 1908 Berlin Convention coming up with wording similar to today's Article 2(3). Gervais's article cites Étude sur la Convention de Berlin de 1908 pour la Protection des Œuvres Littéraires et artistiques by André Petit implying disagreement between the countries about whether or not to protect unlawful derivatives, thus leaving it unsaid. Unfortunately, I'm unable to locate any copies of this source.
Additionally, thanks to a fortunate snippet Google Books displayed, I know that La conférence de Berlin (14 octobre-13 novembre 1908) by Georges-François-Joseph Martin also discusses this exact point on page 187, quoting someone who thought unlawful derivatives would be protected now, though I couldn't get enough context to really determine anything. While I could find available copies of this book, for now it's a little on the expensive side for me.
Overview of various jurisdictions
In the EU, the derivative right is not harmonized and so the question is punted to the Member States. There is no implementation of either Berne Convention Article 2(3) or Article 12 in the Information Society (Copyright) Directive, Article 12 being specifically acknowledged by the Court of Justice in the Allposters case.
In the UK, infringing derivatives are probably protected, see Redwood Music Ltd. v. Chappell & Co. Ltd.,  R.P.C. 109 (Q.B. Div.) at 120. I can't find the judgement text outside a paywall, but an article by William J. Braithwaite (PDF) quotes the relevant part on page 209 (the square brackets are his):
[T]he idea that [the owner of the underlying copyright] should be entitled to reap the benefit of another's original work, by exploiting it, however extensive such work might be, however innocently it might have been made, offends against justice and common sense.
Additionally, the justice noted the argument that unlawful derivatives are not explicitly excluded from copyright protection and that parliament has declined to make this explicit.
If I understand the English court system correctly, this decision was two appeals away from the Supreme Court (House of Lords back then), but there doesn't appear to have been any appeal. For what it's worth though, the justice who issued the decision ultimately became Senior Law Lord.
In Italy, the Supreme Court has determined that derivative works can be simultaneously infringing and protected.