Description
libmspack through 0.11alpha contains an uninitialized pointer free vulnerability in kwajd_open() in mspack/kwajd.c that frees unzeroed filename and extra pointers on header read errors. Attackers can supply a truncated, empty, or wrong-signature KWAJ file to crash the process or obtain an arbitrary-free memory corruption primitive.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| kyz | libmspack | ≤ 0.11alpha | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | libmspack | 0.11-2 | — |
| Debian 13 | libmspack | No fix yet | — |
| Debian 12 | libmspack | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | libmspack | 0.11-1.1ubuntu0.26.10.1 | USN-8973-1 |
| Ubuntu 26.04 LTS | libmspack | 0.11-1.1ubuntu0.26.04.1 | USN-8973-1 |
| Ubuntu 24.04 LTS | libmspack | 0.11-1.1ubuntu0.24.04.1 | USN-8973-1 |
| Ubuntu 22.04 LTS | libmspack | 0.10.1-2ubuntu0.1 | USN-8973-1 |
| Ubuntu 20.04 LTS | libmspack | No fix yet | — |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 18.04 LTS | libmspack | No fix yet | — |
| Ubuntu 16.04 LTS | libmspack | No fix yet | — |
| Ubuntu Pro 14.04 LTS | clamav +1 | No fix yet | — |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | clamav +1 | No fix yet | — |
Advisories 1
- USN-8973-1 libmspack vulnerability Ubuntu Security Notices (USN) · Nov 4, 2026
References
- https://github.com/kyz/libmspack/commit/4d868504114346aa767d435fbb89a8b76603493f patch
- https://github.com/kyz/libmspack/blob/v0.11alpha/libmspack/mspack/kwajd.c#L111-L181 technical-description
- https://hackmd.io/@haind-pwn/libmspack-kwaj-uninitialized-free third-party-advisory
- VulnCheck Advisory: libmspack through 0.11alpha Uninitialized Pointer Free via kwajd_open Error Path third-party-advisory