SpdyStream: DOS on CRI
The SPDY/3 frame parser in spdystream does not validate
attacker-controlled counts and lengths before allocating memory. A
remote peer that can send SPDY frames to a service using spdystream can
cause the process to allocate gigabytes of memory with a small number of
malformed control frames, leading to an out-of-memory crash.
Three allocation paths in the receive side are affected:
1. SETTINGS entry count -- The SETTINGS frame reader reads a 32-bit
numSettings from the payload and allocates a slice of that size
without checking it against the declared frame length. An attacker
can set numSettings to a value far exceeding the actual payload,
triggering a large allocation before any setting data is read.
2. Header count -- parseHeaderValueBlock reads a 32-bit
numHeaders from the decompressed header block and allocates an
http.Header map of that size with no upper bound.
3. Header field size -- Individual header name and value lengths are
read as 32-bit integers and used directly as allocation sizes with
no validation.
Because SPDY header blocks are zlib-compressed, a small on-the-wire
payload can decompress into attacker-controlled bytes that the parser
interprets as 32-bit counts and lengths. A single crafted frame is
enough to exhaust process memory.
Impact
Any program that accepts SPDY connections using spdystream -- directly
or through a dependent library -- is affected. A remote peer that can
send SPDY frames to the service can crash the process with a single
crafted SPDY control frame, causing denial of service.
Affected versions
github.com/moby/spdystream <= v0.5.0
Fix
v0.5.1 addresses the receive-side allocation bugs and adds related
hardening:
Core fixes:
- SETTINGS entry-count validation -- The SETTINGS frame reader now
checks that numSettings is consistent with the declared frame
length (numSettings <= (length-4)/8) before allocating.
- Header count limit --
parseHeaderValueBlock enforces a maximum
number of headers per frame (default: 1000).
- Header field size limit -- Individual header name and value
lengths are checked against a per-field size limit (default: 1 MiB)
before allocation.
- Connection closure on protocol error -- The connection read loop
now closes the underlying net.Conn when it encounters an
InvalidControlFrame error, preventing further exploitation on the
same connection.
Additional hardening:
- Write-side bounds checks -- All frame write methods now verify
that payloads fit within the 24-bit length field, preventing the
library from producing invalid frames.
Configurable limits:
- Callers can adjust the defaults using
NewConnectionWithOptions or
the lower-level spdy.NewFramerWithOptions with functional options:
WithMaxControlFramePayloadSize, WithMaxHeaderFieldSize, and
WithMaxHeaderCount.
