CVE-2026-120251
imagecodecs 2026.3.6 through 2026.10.10 Infinite Loop via ccittfax4_decode()
What happened?
imagecodecs 2026.3.6 through 2026.10.10 contains an infinite loop vulnerability in ccitt_fax4_decode_size() that allows attackers to hang the calling process by supplying a crafted CCITT Group 4 stream. Attackers can provide an 8-byte G4 stream lacking EOFB to ccittfax4_decode() or the numcodecs Ccittfax4 codec, consuming full CPU until the process is killed.
Affected software and versions
| Software | Version information | Fixed version |
|---|---|---|
| imagecodecscgohlke | affected: 2026.3.6 to ≤ 2026.10.10 | See vendor advisory |
Version information comes from the source record and can include unaffected products and exceptions. Distribution packages may contain backported fixes: an older upstream version alone does not prove a server is affected.
Is it being exploited?
This CVE was not listed in the CISA catalogue at our last retrieval. This does not establish that exploitation is absent.
How to respond
- Confirm the product, installed package version, and any configuration requirements in the vendor advisory.
- Follow the vendor’s remediation or workaround guidance in the references below. Structured fixed-version data is unavailable here; the publisher’s description may include a fix or workaround.
- Restart affected services if required, then verify the running version. Known exploitation may warrant investigation as well as patching.
Sources and remediation references
- https://www.cve.org/CVERecord?id=CVE-2026-120251
- https://github.com/cgohlke/imagecodecs/issues/158
- https://github.com/cgohlke/imagecodecs/blob/v2026.10.10/3rdparty/ccitt/ccitt.c#L1449
- https://github.com/cgohlke/imagecodecs
- https://www.vulncheck.com/advisories/imagecodecs-2026.3.6-through-2026.10.10-infinite-loop-via-ccittfax4-decode