Vulnerability-Lookup

CVE-2026-107215 (GCVE-0-2026-107215)

Vulnerability from cvelistv5 – Published: 2026-10-07 17:48 – Updated: 2026-10-10 02:38

Title

Excelize: extractPart allocates attacker-controlled, unbounded and negative-sized buffers from CFB directory entries: remote panic / OOM DoS

Summary

Excelize is a Go language library for reading and writing Microsoft Excel spreadsheets. From 2.3.1 to 2.11.0, extractPart allocates a byte slice directly from an attacker-controlled CFB directory-entry size before validating the sector chain or size domain. extractPart trusts the CFB directory entry streamSize for EncryptionInfo and EncryptedPackage allocations before validating the stream. When a crafted OLE compound file declares a negative or extremely large EncryptionInfo or EncryptedPackage stream size, the declared size reaches make with a negative length or forces a multi-gigabyte allocation, allowing an attacker to panic or exhaust process memory. No fixed version is available as of this review.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-10 02:38 UTC

CWE

CWE-789 - Memory Allocation with Excessive Size Value

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7708 records in the last 180 days details

References

3 references

URL	Tags
https://github.com/qax-os/excelize/security/advis…	x_refsource_CONFIRM
https://github.com/qax-os/excelize/pull/2396	x_refsource_MISC
https://github.com/qax-os/excelize/commit/5f636f9…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
qax-os	excelize	Affected: >= 2.3.1, <= 2.11.0	guessed

Show details on NVD website

JSON

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FKIE_CVE-2026-107215

Vulnerability from fkie_nvd - Published: 2026-10-07 18:17 - Updated: 2026-10-13 14:23

Severity

7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/qax-os/excelize/commit/5f636f9dcde55911f14290060b017f0cc88cd694	Patch
security-advisories@github.com	https://github.com/qax-os/excelize/pull/2396	Issue Tracking, Patch
security-advisories@github.com	https://github.com/qax-os/excelize/security/advisories/GHSA-x2q3-8cjh-766f	Exploit, Vendor Advisory
134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/qax-os/excelize/security/advisories/GHSA-x2q3-8cjh-766f	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	excelize	excelize	*

JSON

To clipboard

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}

GHSA-X2Q3-8CJH-766F

Vulnerability from github – Published: 2026-10-08 16:31 – Updated: 2026-10-08 16:31

Summary

Excelize: extractPart allocates attacker-controlled, unbounded and negative-sized buffers from CFB directory entries: remote panic / OOM DoS

Details

Summary

extractPart allocates directly from the mscfb directory-entry size with no clamping (crypt.go:198, same missing bound at crypt.go:204):

buf := make([]byte, entry.Size)

entry.Size is the raw streamSize field from the attacker-controlled CFB directory entry (mscfb v1.0.8 fixFile, file.go:109-120: full uint64 → int64 for major version 4, low uint32 for v3). mscfb only detects short sector chains later, inside File.Read (file.go:485-489 "emergency brake") — i.e. after the allocation. The zip path already enforces UnzipSizeLimit, and the KDF path bounds work with maxSpinCount; this path consults no limit at all.

Details

Two consequences, both execution-confirmed against pristine master (ecd99d761fe0, 2026-09-08):

Hard crash: a version-4 CFB declaring streamSize = 0xFFFFFFFFFFFFFFFF yields entry.Size == -1 → panic: runtime error: makeslice: len out of range, which escapes Decrypt (openReaderAt converts errors, not panics, excelize.go:210-214) and kills the process.
Memory exhaustion: any CFB (v3 suffices) declaring streamSize up to 0xFFFFFFFF forces up to 4 GiB of zeroed allocation from a ~12 KB file — an amplification factor of ~350,000×, trivially repeated per request in memory-limited deployments.

Call path: OpenFile/OpenReader/OpenBytes → openReaderAt (excelize.go:208-215, OLE magic sniff) → Decrypt (crypt.go:145-150) → extractPart (crypt.go:198).

PoC

A standalone program (public API only) was provided to the maintainer by email (2-extractpart-oom): it builds a valid-enough v4 (4096-byte sector) CFB — header (signature, sector shift 0x0C, DIFAT[0]=1), one directory sector with Root Entry (typeID 5, child=1) and a stream entry EncryptionInfo (objectType=2, startingSector=endOfChain, streamSize=0xFFFFFFFFFFFFFFFF). mscfb.New succeeds, doc.Next() returns the entry, and extractPart calls make([]byte, -1) before any chain validation. On master ecd99d761fe0 the program prints panic: runtime error: makeslice: len out of range; with the proposed patch it prints BLOCKED. An -oom flag demonstrates the 4 GiB allocation variant with streamSize = 0xFFFFFFFF.

Impact

An attacker uploads any file starting with the OLE signature D0 CF 11 E0 A1 B1 1A E1 (~12 KB is enough) to a service that calls excelize.OpenFile/OpenReader/OpenBytes on it (or calls Decrypt directly): remote, unauthenticated process crash (hard panic) or forced 4 GiB allocation per request (OOM) with a ~350,000× amplification factor.

Proposed fix

Bound the declared stream size before allocating in extractPart: reject negative sizes and sizes above a sane policy cap (1 GiB is far above any real encrypted-workbook part) with ErrWorkbookFileFormat, so malformed CFBs are rejected as errors instead of panicking or OOMing. A complete patch has been provided to the maintainer; verified that the patch blocks the PoC while legitimate Encrypt() output still opens.

Severity

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/xuri/excelize/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.3.1"
            },
            {
              "fixed": "2.11.1-0.20260912113515-5f636f9dcde5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-107215"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-789"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-08T16:31:26Z",
    "nvd_published_at": "2026-10-07T18:17:19Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\n`extractPart` allocates directly from the mscfb directory-entry size with no clamping (`crypt.go:198`, same missing bound at `crypt.go:204`):\n\n```go\nbuf := make([]byte, entry.Size)\n```\n\n`entry.Size` is the raw `streamSize` field from the attacker-controlled CFB directory entry (mscfb v1.0.8 `fixFile`, `file.go:109-120`: full uint64 \u2192 int64 for major version 4, low uint32 for v3). mscfb only detects short sector chains later, inside `File.Read` (`file.go:485-489` \"emergency brake\") \u2014 i.e. **after** the allocation. The zip path already enforces `UnzipSizeLimit`, and the KDF path bounds work with `maxSpinCount`; this path consults no limit at all.\n\n### Details\n\nTwo consequences, both execution-confirmed against pristine master (`ecd99d761fe0`, 2026-09-08):\n\n1. **Hard crash**: a version-4 CFB declaring `streamSize = 0xFFFFFFFFFFFFFFFF` yields `entry.Size == -1` \u2192 `panic: runtime error: makeslice: len out of range`, which escapes `Decrypt` (`openReaderAt` converts errors, not panics, `excelize.go:210-214`) and kills the process.\n2. **Memory exhaustion**: any CFB (v3 suffices) declaring `streamSize` up to `0xFFFFFFFF` forces up to 4 GiB of zeroed allocation from a ~12 KB file \u2014 an amplification factor of ~350,000\u00d7, trivially repeated per request in memory-limited deployments.\n\nCall path: `OpenFile`/`OpenReader`/`OpenBytes` \u2192 `openReaderAt` (`excelize.go:208-215`, OLE magic sniff) \u2192 `Decrypt` (`crypt.go:145-150`) \u2192 `extractPart` (`crypt.go:198`).\n\n### PoC\n\nA standalone program (public API only) was provided to the maintainer by email (`2-extractpart-oom`): it builds a valid-enough v4 (4096-byte sector) CFB \u2014 header (signature, sector shift `0x0C`, `DIFAT[0]=1`), one directory sector with Root Entry (typeID 5, child=1) and a stream entry `EncryptionInfo` (objectType=2, startingSector=endOfChain, `streamSize=0xFFFFFFFFFFFFFFFF`). `mscfb.New` succeeds, `doc.Next()` returns the entry, and `extractPart` calls `make([]byte, -1)` before any chain validation. On master `ecd99d761fe0` the program prints `panic: runtime error: makeslice: len out of range`; with the proposed patch it prints BLOCKED. An `-oom` flag demonstrates the 4 GiB allocation variant with `streamSize = 0xFFFFFFFF`.\n\n### Impact\n\nAn attacker uploads any file starting with the OLE signature `D0 CF 11 E0 A1 B1 1A E1` (~12 KB is enough) to a service that calls `excelize.OpenFile`/`OpenReader`/`OpenBytes` on it (or calls `Decrypt` directly): remote, unauthenticated process crash (hard panic) or forced 4 GiB allocation per request (OOM) with a ~350,000\u00d7 amplification factor.\n\n### Proposed fix\n\nBound the declared stream size before allocating in `extractPart`: reject negative sizes and sizes above a sane policy cap (1 GiB is far above any real encrypted-workbook part) with `ErrWorkbookFileFormat`, so malformed CFBs are rejected as errors instead of panicking or OOMing. A complete patch has been provided to the maintainer; verified that the patch blocks the PoC while legitimate `Encrypt()` output still opens.",
  "id": "GHSA-x2q3-8cjh-766f",
  "modified": "2026-10-08T16:31:26Z",
  "published": "2026-10-08T16:31:26Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/qax-os/excelize/security/advisories/GHSA-x2q3-8cjh-766f"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-107215"
    },
    {
      "type": "WEB",
      "url": "https://github.com/qax-os/excelize/pull/2396"
    },
    {
      "type": "WEB",
      "url": "https://github.com/qax-os/excelize/commit/5f636f9dcde55911f14290060b017f0cc88cd694"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/qax-os/excelize"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Excelize: extractPart allocates attacker-controlled, unbounded and negative-sized buffers from CFB directory entries: remote panic / OOM DoS"
}

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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CVE-2026-107215 (GCVE-0-2026-107215)

FKIE_CVE-2026-107215

GHSA-X2Q3-8CJH-766F

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