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authorDavid Kalnischkies <david@kalnischkies.de>2015-05-18 22:15:06 +0200
committerDavid Kalnischkies <david@kalnischkies.de>2015-05-18 22:15:06 +0200
commit6bf93605fdb8e858d3f0a79a124c1d39f760094d (patch)
tree4f1fb6549db04d6b39845e8587316460b493f249 /apt-pkg/aptconfiguration.h
parent8eafc759544298211cd0bfaa3919afc0fadd47d1 (diff)
treat older Release files than we already have as an IMSHit
Valid-Until protects us from long-living downgrade attacks, but not all repositories have it and an attacker could still use older but still valid files to downgrade us. While this makes it sounds like a security improvement now, its a bit theoretical at best as an attacker with capabilities to pull this off could just as well always keep us days (but in the valid period) behind and always knows which state we have, as we tell him with the If-Modified-Since header. This is also why this is 'silently' ignored and treated as an IMSHit rather than screamed at the user as this can at best be an annoyance for attackers. An error here would 'regularily' be encountered by users by out-of-sync mirrors serving a single run (e.g. load balancer) or in two consecutive runs on the other hand, so it would just help teaching people ignore it. That said, most of the code churn is caused by enforcing this additional requirement. Crisscross from InRelease to Release.gpg is e.g. very unlikely in practice, but if we would ignore it an attacker could sidestep it this way.
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