CVE-2025-57807: Magick.NET Q16 x64 · ImageMagick BlobStream Forward-Seek Under-Allocation

**Reporter:** Lumina Mescuwa **Product:** ImageMagick 7 (MagickCore) **Component:** `MagickCore/blob.c` (Blob I/O - BlobStream) **Tested:** 7.1.2-0 (source tag) and 7.1.2-1 (Homebrew), macOS arm64, clang-17, Q16-HDRI **Impact:** Heap out-of-bounds **WRITE** (attacker-controlled bytes at attacker-chosen offset) → memory corruption; potential code execution --- ## Executive Summary For memory-backed blobs (**BlobStream**), [`SeekBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5106-L5134) permits advancing the stream **offset** beyond the current end without increasing capacity. The subsequent [`WriteBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5915-L5938) then expands by **`quantum + length`** (amortized) instead of **`offset + length`**, and copies to `data + offset`. When `offset ≫ extent`, the copy targets memory beyond the allocation, producing a deterministic heap write on 64-bit builds. No 2⁶⁴ arithmetic wrap, external delegates, or policy settings are required. --- ## Affected Scope - **Versions confirmed:** 7.1.2-0, 7.1.2-1 - **Architectures:** Observed on macOS arm64; architecture-agnostic on LP64 - Paths: MagickCore blob subsystem — **BlobStream** ([`SeekBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5106-L5134) and [`WriteBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5915-L5938)). - **Not required:** External delegates; special policies; integer wraparound --- ## Technical Root Cause **Types (LP64):** `offset: MagickOffsetType` (signed 64-bit) `extent/length/quantum: size_t` (unsigned 64-bit) `data: unsigned char*` **Contract mismatch:** - [`SeekBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5106-L5134) (BlobStream) updates `offset` to arbitrary positions, including past end, **without** capacity adjustment. - [`WriteBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5915-L5938) tests `offset + length >= extent` and grows **by** `length + quantum`, doubles `quantum`, reallocates to `extent + 1`, then: ``` q = data + (size_t)offset; memmove(q, src, length); ``` There is **no guarantee** that `extent ≥ offset + length` post-growth. With `offset ≫ extent`, `q` is beyond the allocation. **Wrap-free demonstration:** Initialize `extent=1`, write one byte (`offset=1`), seek to `0x10000000` (256 MiB), then write 3–4 bytes. Growth remains << `offset + length`; the copy overruns the heap buffer. --- ## Exploitability & Reachability - **Primitive:** Controlled bytes written at a controlled displacement from the buffer base. - **Reachability:** Any encode-to-memory flow that forward-seeks prior to writing (e.g., header back-patching, reserved-space strategies). Even if current encoders/writers avoid this, the API contract **permits** it, thus creating a latent sink for first- or third-party encoders/writers. - **Determinism:** Once a forward seek past end occurs, the first subsequent write reliably corrupts memory. --- ## Impact Assessment - **Integrity:** High - adjacent object/metadata overwrite plausible. - **Availability:** High - reliably crashable (ASan and non-ASan). - **Confidentiality:** High - Successful exploitation to RCE allows the attacker to read all data accessible by the compromised process. - **RCE plausibility:** Typical of heap OOB writes in long-lived image services; allocator/layout dependent. --- ## CVSS v3.1 Rationale (9.8) - **AV:N / PR:N / UI:N** - server-side image processing is commonly network-reachable without auth or user action. - **AC:L** - a single forward seek + write suffices; no races or specialized state. - **S:U** - corruption localized to the ImageMagick process. - **C:H / I:H / A:H** - A successful exploit leads to RCE, granting full control over the process. This results in a total loss of Confidentiality (reading sensitive data), Integrity (modifying files/data), and Availability (terminating the service). _Base scoring assumes successful exploitation; environmental mitigations are out of scope of Base metrics._ --- ## Violated Invariant > **Before copying `length` bytes at `offset`, enforce `extent ≥ offset + length` with overflow-checked arithmetic.** The BlobStream growth policy preserves amortized efficiency but fails to enforce this **per-write** safety invariant. --- ## Remediation (Principle) In [`WriteBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5915-L5938) (BlobStream case): 1. **Checked requirement:** `need = (s

• github.com/ImageMagick/ImageMagick/security/advisories/GHSA-23hg-53q6-hqfg (opens in a new tab)
• nvd.nist.gov/vuln/detail/CVE-2025-57807 (opens in a new tab)
• github.com/ImageMagick/ImageMagick/commit/077a417a19a5ea8c85559b602754a5b928eef23e (opens in a new tab)
• github.com/ImageMagick/ImageMagick (opens in a new tab)
• lists.debian.org/debian-lts-announce/2025/09/msg00012.html (opens in a new tab)

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