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CVE-2026-22691· NVD / CVE Program· CNA GitHub_M

pypdf has possible long runtimes for malformed startxref

pypdf is a free and open-source pure-python PDF library. Prior to version 6.6.0, pypdf has possible long runtimes for malformed startxref. An attacker who uses this vulnerability can craft a PDF which leads to possibly long runtimes for invalid startxref entries. When rebuilding the cross-reference table, PDF files with lots of whitespace characters become problematic. Only the non-strict reading mode is affected. Only the non-strict reading mode is affected. This issue has been patched in version 6.6.0.

LowCVSS 2.7 · v4.0—No exploit Fix available
Published
Jan 10, 2026
Updated
Jun 17, 2026
EPSS
0.4% · 36th percentile
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Action score

10

Monitor

Low priority for now.

CVSS
10 / 40 · 2.7 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
2.7
NVD has not scored this yet; the score shown is the CNA’s.

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

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Affected systems

VendorProduct
pypdf projectpypdf

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • pypdf project pypdfbefore 6.6.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • py-pdf pypdf

    • < 6.6.0affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12pypdfall versions—
Debian:12pypdf2all versions—
Debian:14pypdfbefore 6.9.0-16.9.0-1
PyPIpypdfbefore 6.6.06.6.0

Same product

pypdf project: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-103000pypdf: Possible large memory usage when retrieving alphabetical page labels
    34Monitor
  • CVE-2026-102999pypdf: Possible long runtimes with large amount of embedded files
    34Monitor
  • CVE-2026-102998pypdf: Possible long runtimes when generating appearance streams
    34Monitor
  • CVE-2026-102997pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)
    34Monitor
  • CVE-2026-102996pypdf: Possible large memory usage when parsing font data
    34Monitor
  • CVE-2026-102995pypdf: Possible large memory usage for large /ToUnicode streams (Follow-up 2)
    34Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
py-pdf pypdf6.6.0 · descriptionVendor (CNA)
debian:pypdf6.9.0-1 · Debian:14Package registry (OSV)
PyPI:pypdf6.6.0Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-59936179 days apartpypdf: Possible infinite loop for not terminated inline images
    34Monitor
  • CVE-2026-102993263 days apartpypdf: Possible large memory usage when retrieving Roman page labels
    34Monitor
  • CVE-2026-102996263 days apartpypdf: Possible large memory usage when parsing font data
    34Monitor
  • CVE-2026-102998263 days apartpypdf: Possible long runtimes when generating appearance streams
    34Monitor
  • CVE-2026-102999263 days apartpypdf: Possible long runtimes with large amount of embedded files
    34Monitor
  • CVE-2026-103000263 days apartpypdf: Possible large memory usage when retrieving alphabetical page labels
    34Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

ts
function expand(node) {  return node.children.map(expand);}

Fixed

ts
const MAX_DEPTH = 32;function expand(node, depth = 0) {  if (depth > MAX_DEPTH) throw new Error("too deep");  return node.children.map((c) => expand(c, depth + 1));}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records