CVE-2026-39886

#!/usr/bin/env python3 """ PoC for CVE-2026-39886: OpenEXR Signed Integer Overflow in ht_undo_impl() This script attempts to generate a crafted OpenEXR file. Trigger conditions: 16,385 FLOAT channels, Width 32,767. """ import struct def generate_malformed_exr(): # Note: Creating a valid EXR header with 16385 channels programmatically is complex. # This demonstrates the calculation logic that leads to the overflow. width = 32767 # Max HTJ2K width num_channels = 16385 # Number of FLOAT channels mentioned in CVE bytes_per_float = 4 # sizeof(float) # Vulnerable calculation simulation # bpl = width * num_channels * bytes_per_float bpl = width * num_channels * bytes_per_float print(f"Width: {width}") print(f"Channels: {num_channels}") print(f"Calculated BPL (unsigned): {bpl}") print(f"Max INT (signed 32-bit): {2**31 - 1}") if bpl > 2**31 - 1: print("[+] Integer Overflow condition met!") # Simulate signed 32-bit overflow signed_bpl = struct.unpack('>i', struct.pack('>I', bpl & 0xFFFFFFFF))[0] print(f"Overflowed BPL (signed 32-bit): {signed_bpl}") if __name__ == "__main__": generate_malformed_exr()

{"cve": {"id": "CVE-2026-39886", "sourceIdentifier": "[email protected]", "published": "2026-04-21T02:16:07.753", "lastModified": "2026-04-22T18:41:18.187", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "OpenEXR provides the specification and reference implementation of the EXR file format, an image storage format for the motion picture industry. Versions 3.4.0 through 3.4.9 have a signed integer overflow vulnerability in OpenEXR's HTJ2K (High-Throughput JPEG 2000) decompression path. The `ht_undo_impl()` function in `src/lib/OpenEXRCore/internal_ht.cpp` accumulates a bytes-per-line value (`bpl`) using a 32-bit signed integer with no overflow guard. A crafted EXR file with 16,385 FLOAT channels at the HTJ2K maximum width of 32,767 causes `bpl` to overflow `INT_MAX`, producing undefined behavior confirmed by UBSan. On an\nallocator-permissive host where the required ~64 GB allocation succeeds, the wrapped negative `bpl` value would subsequently be used as a per-scanline pointer advance, which would produce a heap out-of-bounds write. On a memory-constrained host, the allocation fails before `ht_undo_impl()` is entered. This is the second distinct integer overflow in `ht_undo_impl()`. CVE-2026-34545 addressed a different overflow in the same function — the `int16_t p` pixel-loop counter at line ~302 that overflows when iterating over channels whose `width` exceeds 32,767. The CVE-2026-34545 fix did not touch the `int bpl` accumulator at line 211, which is the subject of this advisory. The `bpl` accumulator was also not addressed by any of the 8 advisories in the 2026-04-05 v3.4.9 release batch. This finding is structurally identical to CVE-2026-34588 (PIZ `wcount*nx` overflow in `internal_piz.c`) and should be remediated with the same pattern. The CVE-2026-34588 fix did not touch `internal_ht.cpp`. Version 3.4.10 contains a remediation that addresses the vulnerability in `internal_ht.cpp`."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "baseScore": 5.3, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "LOW"}, "exploitabilityScore": 3.9, "impactScore": 1.4}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-190"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:openexr:openexr:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.4.0", "versionEndExcluding": "3.4.10", "matchCriteriaId": "7AEDBB28-BFC6-427E-977B-A26211BC5724"}]}]}], "references": [{"url": "https://github.com/AcademySoftwareFoundation/openexr/releases/tag/v3.4.10", "source": "[email protected]", "tags": ["Product", "Release Notes"]}, {"url": "https://github.com/AcademySoftwareFoundation/openexr/security/advisories/GHSA-r3mr-mx8q-jcw5", "source": "[email protected]", "tags": ["Exploit", "Mitigation", "Vendor Advisory"]}]}}