CVE-2026-96596: erl_tar:extract/2 loops forever on a GNU sparse member with a trailing hole
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 stdlib from 8.0 before 8.1.1, and rebar3 from 3.27.1 onward, and hex from 2.4.2 onward; hexcore: from 0.14.0 onward.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Erlang/OTPto a version that resolves this vulnerability.Fixed in 29.1.2 - Upgrade
Upgrade
Erlang stdlibto a version that resolves this vulnerability.Fixed in 8.1.1 - Configuration
Use the memory option for extraction; extraction with this option is not affected.
erl_tar extraction memory = enabled - Configuration
Set the {max_size, N} option with N below the real size of the GNU sparse member to prevent the infinite loop.
erl_tar extraction max_size = N below the real size of the member
Event History
Frequently Asked Questions
Which extraction paths are affected?
The issue affects erl_tar:extract/1,2 when a GNU sparse member is written to disk. Extraction using the memory option is not affected.
What must an attacker provide to trigger the denial of service?
An attacker must be able to supply a crafted tar archive containing a GNU sparse member whose sparse map ends before the member's real size. A 2048-byte archive is sufficient to keep the extracting process and one scheduler busy until the process is killed.
Does the max_size option mitigate the issue?
Only if max_size is set below the real size of the crafted member. It does not prevent the loop when the configured limit permits the member's real size.
Are Hex and rebar3 affected only through the Erlang standard library?
No. hex_core includes its own copy of erl_tar as hex_erl_tar, and Hex and rebar3 ship that code under the mix_hex_erl_tar and r3_hex_erl_tar module names. These copies contain the same vulnerable code and do not call stdlib's erl_tar.