Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in Erlang OTP stdlib (erltar module), hexpm hexcore (hexerltar module), hexpm hex (mixhexerltar module) and erlang rebar3 (r3hexerltar module) allows an attacker who supplies a tar archive to cause a denial of service via a crafted GNU sparse member.

When erltar:extract/1,2 writes a member to disk, erltar:streamtofileloop/3 reads it in chunks of 65536 bytes by default. For a GNU sparse member whose sparse map ends before its real size, erltar:dosparseread/3 matches its trailing-hole clause before its zero-length clause. After the chunk is used up, the trailing-hole clause reads zero bytes, does not advance the position, and recurses forever. A 2048-byte archive keeps the extracting process and one scheduler busy until the process is killed. The {maxsize, N} option prevents this only when N is below the real size of the member. Extraction with the memory option is not affected.

hexcore ships its own copy of erltar as hexerltar, and Hex and rebar3 ship hexcore with prefixed module names (mixhexerltar and r3hexerltar). These copies contain the same code and do not call stdlib's erltar, so they are affected on any OTP version. OTP 28 is not affected, but an application running on OTP 28 is affected if it extracts archives through an affected version of hexcore, Hex or rebar3.

This issue affects OTP from OTP 29.0 before OTP 29.1.2, corresponding to rebar3 from 3.27.1 before 3.28.0, and stdlib from 8.0 before 8.1.1, and hex from 2.4.2 before 2.5.3; hexcore: from 0.14.0 before 0.20.1.

Impact

The Hex client (hexcore) deserializes Erlang terms received from the Hex API using binarytoterm/1 without sufficient restrictions.

If an attacker can control the HTTP response body returned by the Hex API, this allows denial-of-service attacks such as atom table exhaustion, leading to a VM crash. No released versions are known to allow remote code execution.

Patches

https://github.com/hexpm/hexcore/commit/cdf726095bca85ad2549d146df1e831ae93c2b13 https://github.com/hexpm/hex/commit/636739f3322514e9303ca335fb630696fcbb3c95 https://github.com/erlang/rebar3/commit/1d4478f527e373de0b225951e53115450e0d9b9d

Workarounds

Ensure that the Hex API URL (HEXAPIURL) points only to trusted endpoints. There is no client-side workaround that fully mitigates this issue without applying the patch.

Resources

hexcore Module: https://github.com/hexpm/hexcore/blob/main/src/hexapi.erl Hex Vendored Module: https://github.com/hexpm/hex/blob/main/src/mixhexapi.erl Rebar3 Vendored Module: https://github.com/erlang/rebar3/blob/main/apps/rebar/src/vendored/r3hexapi.erl hexcore Patch: https://github.com/hexpm/hexcore/commit/cdf726095bca85ad2549d146df1e831ae93c2b13 Hex Vendored Patch: https://github.com/hexpm/hex/commit/636739f3322514e9303ca335fb630696fcbb3c95 Rebar3 Vendored Patch: https://github.com/erlang/rebar3/commit/1d4478f527e373de0b225951e53115450e0d9b9d