Description
HTSlib through 1.24 contains a heap out-of-bounds write and read vulnerability in bgzf_index_load_hfile() in bgzf.c that allows attackers to corrupt heap memory by supplying a crafted .gzi index entry count. A count of 0xFFFFFFFF truncates noffs to zero, causing writes past a malloc(0) buffer and an offs[-1] read in bgzf_useek(), resulting in heap corruption or crashes in tools like samtools and bcftools.
References7
- github.com/samtools/htslib
- github.com/samtools/htslib/blob/1.24/bgzf.c#L2504
- github.com/samtools/htslib/commit/18dddf02bb2c0053b32acec427723…
- github.com/samtools/htslib/issues/2113
- github.com/samtools/htslib/pull/2057
- hackmd.io/@haindpwn/htslib-bgzf-gzi-int-truncation-oob
- www.vulncheck.com/advisories/htslib-through-1.24-heap-out-of-bo…
Metrics
- CVSS 3.1
-
4.4
MEDIUM
Score source: CNA
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:L - CVSS 4.0
-
4.8
MEDIUM
Score source: CNA
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 2 · as of 8 November 2026
- CWE
- CWE-197
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.