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High, CVSS 7.5amended

ImageSharp: CCITT fax decompression (T4/Modified Huffman): unbounded WriteBits overflows strip buffer — heap OOB write in SixLabors.ImageSharp

CVE-2026-106117GHSA-jj3q-cwqj-842r

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (imagesharp 4.1.1, 3.2.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • NuGet imagesharp

    Affected
    >= 3.0.0, < 3.2.0>= 4.0.0, < 4.1.1
    Fixed in
    3.2.0, 4.1.1

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-106117: 0.39% estimated exploitation activity in the next 30 days; percentile 32.66 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary When decoding a fax-compressed strip TIFF (Compression=3 / Group 3 1D, or Compression=2 / Modified Huffman), the CCITT decompressors write decoded runs through BitWriterUtils.WriteBits/WriteBit/WriteZeroBit, which advance and write bits via Unsafe.Add with read-modify-write semantics — without ever comparing the write position against the target buffer length. The strip buffer is sized ImageWidth × RowsPerStrip (8 bytes in the PoC), but two independent defects let an attacker write tens of millions of bits past it: (a) T4 only increments rowsWritten when an EOL code is read, and one ReadNextRun accumulates unlimited makeup codes (+2560 px per 12-bit code) into a single RunLength that WritePixelRun then writes in one shot; (b) Modified Huffman writes before validating (pixelsWritten Width is checked at :90-93, after the write at :56-63), so the overflow completes even though an exception is thrown later. One crafted ~90 KB file writes ~19.2 MB linearly past an 8-byte buffer…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-jj3q-cwqj-842r

  2. Revision 1 · created ·

    Published from osv record GHSA-jj3q-cwqj-842r

Agent brief

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# Patch Next advisory brief: CVE-2026-106117

Advisory: ImageSharp: CCITT fax decompression (T4/Modified Huffman): unbounded WriteBits overflows strip buffer — heap OOB write in SixLabors.ImageSharp
IDs: CVE-2026-106117, GHSA-jj3q-cwqj-842r
Record: https://patchnext.com/advisories/cve-2026-106117 (revision 2, source checked 26 Oct 2026, 17:05 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: imagesharp 4.1.1, 3.2.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet imagesharp: affected >= 3.0.0, < 3.2.0; >= 4.0.0, < 4.1.1; fixed in 3.2.0, 4.1.1

## Suggested inspection (read-only)
- NuGet imagesharp: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on imagesharp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-jj3q-cwqj-842r (OSV record GHSA-jj3q-cwqj-842r lists affected ranges: NuGet imagesharp >=3.0.0 =4.0.0 <4.1.1 (fixed))
- Verified: https://github.com/advisories/GHSA-jj3q-cwqj-842r (GitHub-reviewed advisory GHSA-jj3q-cwqj-842r lists affected ranges: NuGet imagesharp >=3.0.0 =4.0.0 <4.1.1)

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