CVE-2020-26235

Impact

Unix-like operating systems may segfault due to dereferencing a dangling pointer in specific circumstances. This requires an environment variable to be set in a different thread than the affected functions. This may occur without the user's knowledge, notably in a third-party library.

The affected functions from time 0.2.7 through 0.2.22 are:

• time::UtcOffset::localoffsetat
• time::UtcOffset::trylocaloffset_at
• time::UtcOffset::currentlocaloffset
• time::UtcOffset::trycurrentlocal_offset
• time::OffsetDateTime::now_local
• time::OffsetDateTime::trynowlocal

The affected functions in time 0.1 (all versions) are:

• at
• at_utc
• now

Non-Unix targets (including Windows and wasm) are unaffected.

Patches

In some versions of time, the internal method that determines the local offset has been modified to always return None on the affected operating systems. This has the effect of returning an Err on the try_* methods and UTC on the non-try_* methods. In later versions, time will attempt to determine the number of threads running in the process. If the process is single-threaded, the call will proceed as its safety invariant is upheld.

Users and library authors with time in their dependency tree must perform cargo update, which will pull in the updated, unaffected code.

Users of time 0.1 do not have a patch and must upgrade to an unaffected version: time 0.2.23 or greater or the 0.3 series.

Workarounds

Library authors must ensure that the program only has one running thread at the time of calling any affected method. Binary authors may do the same and/or ensure that no other thread is actively mutating the environment.

References

time-rs/time#293.