Impact

The affected functions set environment variables without synchronization. On Unix-like operating systems, this can crash in multithreaded programs. Programs may segfault due to dereferencing a dangling pointer if an environment variable is read in a different thread than the affected functions. This may occur without the user's knowledge, notably in the Rust standard library or third-party libraries.

The affected functions from time 0.2.7 through 0.2.22 are:

• time::UtcOffset::local_offset_at
• time::UtcOffset::try_local_offset_at
• time::UtcOffset::current_local_offset
• time::UtcOffset::try_current_local_offset
• time::OffsetDateTime::now_local
• time::OffsetDateTime::try_now_local

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

• time::at_utc
• time::at
• time::now
• time::tzset

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

Patches

Pending a proper fix, 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.

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

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

Workarounds

A possible workaround for crates affected through the transitive dependency in chrono, is to avoid using the default oldtime feature dependency of the chrono crate by disabling its default-features and manually specifying the required features instead.

Examples:

Cargo.toml:

chrono = { version = "0.4", default-features = false, features = ["serde"] }

chrono = { version = "0.4.22", default-features = false, features = ["clock"] }

Commandline:

cargo add chrono --no-default-features -F clock

Sources:

• chronotope/chrono#602 (comment)
• vityafx/serde-aux#21

If an attacker is able to flood the network with pairs of HEADERS/RST_STREAM frames, such that the h2 application is not able to accept them faster than the bytes are received, the pending accept queue can grow in memory usage. Being able to do this consistently can result in excessive memory use, and eventually trigger Out Of Memory.

This flaw is corrected in hyperium/h2#668, which restricts remote reset stream count by default.

When this crate is given a pathological certificate chain to validate, it will spend CPU time exponential with the number of candidate certificates at each step of path building.

Both TLS clients and TLS servers that accept client certificate are affected.

This was previously reported in https://github.com/briansmith/webpki/issues/69 and re-reported recently by Luke Malinowski.

webpki 0.22.1 included a partial fix and webpki 0.22.2 added further fixes.

An attacker with an HTTP/2 connection to an affected endpoint can send a steady stream of invalid frames to force the generation of reset frames on the victim endpoint. By closing their recv window, the attacker could then force these resets to be queued in an unbounded fashion, resulting in Out Of Memory (OOM) and high CPU usage.

This fix is corrected in hyperium/h2#737, which limits the total number of internal error resets emitted by default before the connection is closed.

An attacker can send a flood of CONTINUATION frames, causing h2 to process them indefinitely. This results in an increase in CPU usage.

Tokio task budget helps prevent this from a complete denial-of-service, as the server can still respond to legitimate requests, albeit with increased latency.

More details at "https://seanmonstar.com/blog/hyper-http2-continuation-flood/.

Patches available for 0.4.x and 0.3.x versions.

If a close_notify alert is received during a handshake, complete_io does not terminate.

Callers which do not call complete_io are not affected.

rustls-tokio and rustls-ffi do not call complete_io and are not affected.

rustls::Stream and rustls::StreamOwned types use complete_io and are affected.

The h2 crate, used internally by hyper, had a flaw that would accept and queue empty DATA frames without limit. If streams were not actively drained, this could lead to unbounded memory usage, or a panic if the length overflows.

Low severity.

Patched in v0.4.16.