CVE-2026-31970 HTSlib BGZF index file reader has a heap buffer overflow
An integer overflow in HTSlib's GZI index loader allows heap buffer overflows, potentially leading to arbitrary code execution or crashes when processing malicious files.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-31970?
CVE-2026-31970 is a high-severity vulnerability in samtools htslib, published on 18 Mar 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
HTSlib is a library for reading and writing bioinformatics file formats. GZI files are used to index block-compressed GZIP [BGZF] files. In the GZI loading function, `bgzf_index_load_hfile()`, it was possible to trigger an integer overflow, leading to an under- or zero-sized buffer being allocated to store the index. Sixteen zero bytes would then be written to this buffer, and, depending on the result of the overflow the rest of the file may also be loaded into the buffer as well. If the function did attempt to load the data, it would eventually fail due to not reading the expected number of records, and then try to free the overflowed heap buffer. Exploiting this bug causes a heap buffer overflow. If a user opens a file crafted to exploit this issue, it could lead to the program crashing, or overwriting of data and heap structures in ways not expected by the program. It may be possible to use this to obtain arbitrary code execution. Versions 1.23.1, 1.22.2 and 1.21.1 include fixes for this issue. The easiest work-around is to discard any `.gzi` index files from untrusted sources, and use the `bgzip -r` option to recreate them.
Which versions are affected by CVE-2026-31970?
It affects 1 product.
Products include Htslib Htslib.
How do I fix CVE-2026-31970?
Upgrade to a fixed version.
Is CVE-2026-31970 being exploited?
There is no known exploitation of CVE-2026-31970 in the wild and no public exploit code.
Other vulnerabilities in samtools htslib
- CVE-2018-13845 Memory corruption in n/a
- CVE-2017-1000206 Memory corruption in n/a
- CVE-2026-31962 HTSlib CRAM reader has heap buffer overflow due to improper validation of input
- CVE-2026-31963 HTSlib CRAM reader has heap buffer overflow due to improper validation of input
- CVE-2026-31968 HTSlib CRAM decoder vulnerable to buffer overflow
Sources
Also known as DEBIAN-CVE-2026-31970, GHSA-p345-84hx-fq6q, UBUNTU-CVE-2026-31970.