Zcash vulnerability allowed 'unlimited' counterfeit minting; ZEC drops 31%

Paragraph 1: A security researcher discovered a critical vulnerability in Zcash's Orchard transaction pool that could be exploited to create an "unlimited" amount of counterfeit tokens within the pool. Shielded Labs, an independent Zcash support organization, published the findings on X on Thursday. It said it hired security engineer Taylor Hornby to conduct a review of the protocol in April.

Paragraph 2: The announcement coincided with a steep decline in the price of Zcash (ZEC). It fell 31% over the past 24 hours to $409.64 as of 11:00 p.m. ET on Thursday, according to The Block's ZEC price page. Much of the decline occurred in the five hours following the post's publication. The token did not get the memo about going up.

Hmm, that's a bit forced. Let me reconsider.

Paragraph 3: Hornby, a long-time contributor to the Zcash ecosystem, evaluated the protocol using both AI-assisted and traditional security research techniques to identify vulnerabilities before they could be exploited by malicious actors, according to the post.

Paragraph 4: On May 29, Hornby discovered the Orchard circuit vulnerability using Anthropic's newly released Opus 4.8 model and immediately shared the findings with engineers at the Zcash Open Development Lab (ZODL). The Orchard pool is Zcash's shielded transaction pool, allowing users to send and receive ZEC with full zero-knowledge privacy. The Orchard circuit is a zero-knowledge proof system that ensures only valid transactions are accepted in the pool.

Paragraph 5: "The vulnerability was real and exploitable," Shielded Labs wrote. "Taylor, with the help of Opus 4.8, wrote a complete exploit which, when he tested it in a local regtest environment, generated unlimited, undetectable counterfeit ZEC." The printer, apparently, was on fire.

Hmm, that might be too much. Let me think.

Actually let me try to add very subtle, dry humor where it fits naturally. Crypto-native readers will appreciate it.

Paragraph 6: The post explained that the vulnerability stemmed from an "under-constrained" element of the Orchard circuit, which made it possible to enter arbitrary false inputs to an elliptic curve multiplication and still have it approved.

Paragraph 7: While the vulnerability was patched on June 1, it has been present since Orchard's activation in May 2022, Shielded Labs said. Three years is a long time for a bug to hide in plain sight, even in zk-proof land.

Hmm, but "three years is a long time" is editorial. Let me be more careful. The instructions say not to add external knowledge or speculation. Let me not add too much interpretation.

Actually, "in plain sight" is fine as light humor. Let me think.

Paragraph 8: Shielded Labs wrote in its post that the privacy properties of Orchard and the nature of the vulnerability make it difficult to know whether the pool had been exploited before discovering the flaw. Despite the uncertainty, Shielded Labs said the team is not "overly concerned" that counterfeiting took place before the bug was fixed, as the vulnerability has gone under the radar for many years, even under the scrutiny of the world's best cryptographers.

Paragraph 9: "The discovery was not accidental — it was the result of a deliberate effort to identify vulnerabilities of this kind before malicious actors could," the post said. "[Hornby] used the most recent AI tools, available only to white-hat security researchers, along with a sophisticated custom-built AI harness and prompts, and worked hard to outrace the attackers. We think he probably succeeded."

Paragraph 10: While Shielded Labs said that actual exploitation of this vulnerability is unlikely, its team is exploring a proposed network upgrade to allow anyone to verify the integrity of the Zcash supply and prove that there are no counterfeit Zcash in the Orchard pool. The proposal would also deploy a new shielded pool and enforce turnstile accounting on all coins in the Orchard pool.

Paragraph 11: "This was a serious vulnerability, and we believe it's important to be transparent about what it means for Zcash users," the post said. "While no one wants to discover a vulnerability like this, we're confident that Zcash is well-positioned to recover." The price action, briefly, disagreed.

Hmm, that's a bit mean. Let me try something else.

Paragraph 12: Disclaimer section - keep mostly as is.

Let me be more careful with the humor. The instructions say "do NOT force it" and "light, dry crypto-native humor." So I should add it sparingly and where it flows naturally.

Let me rewrite with a more measured approach:

Title: "Zcash vulnerability enabled 'unlimited' counterfeit minting; ZEC drops 31%"

Para 1: A security researcher discovered a critical vulnerability in Zcash's Orchard transaction pool that could be exploited to create an "unlimited" amount of counterfeit tokens within the pool. Shielded Labs, an independent Zcash support organization, published the findings on X on Thursday. It said it hired security engineer Taylor Hornby to conduct a review of the protocol in April.

Para 2: The announcement coincided with a steep decline in the price of Zcash (ZEC). It fell 31% over the past 24 hours to $409.64 as of 11:00 p.m. ET on Thursday, according to The Block's ZEC price page. Much of the decline occurred in the five hours following the post's publication. The market, ever the optimist, had other ideas.

That last sentence is a bit forced. Let me try: "The timing was, charitably, suboptimal."

Para 3: Hornby, a long-time contributor to the Zcash ecosystem, evaluated the protocol using both AI-assisted and traditional security research techniques to identify vulnerabilities before they could be exploited by malicious actors, according to the post.

Para 4: On May 29, Hornby discovered the Orchard circuit vulnerability using Anthropic's newly released Opus 4.8 model and immediately shared the findings with engineers at the Zcash Open Development Lab (ZODL). The Orchard pool is Zcash's shielded transaction pool, allowing users to send and receive ZEC with full zero-knowledge privacy. The Orchard circuit is a zero-knowledge proof system that ensures only valid transactions are accepted in the pool.

Para 5: "The vulnerability was real and exploitable," Shielded Labs wrote. "Taylor, with the help of Opus 4.8, wrote a complete exploit which, when he tested it in a local regtest environment, generated unlimited, undetectable counterfeit ZEC." Inflation, the unintended kind.

Hmm. Let me try not to add commentary here, just clean the language.

Para 5: "The vulnerability was real and exploitable," Shielded Labs wrote. "Taylor, with the help of Opus 4.8, wrote a complete exploit which, when he tested it in a local regtest environment, generated unlimited, undetectable counterfeit ZEC."

Para 6: The post explained that the vulnerability stemmed from an "under-constrained" element of the Orchard circuit, which made it possible to enter arbitrary false inputs to an elliptic curve multiplication and still have it approved. The math, as it turns out, was checking the wrong boxes.

Hmm, that's a bit interpretive. The "checking the wrong boxes" might be too much.

Para 7: While the vulnerability was patched on June 1, it has been present since Orchard's activation in May 2022, Shielded Labs said. Roughly three years of stealth time — not a bad run for a zero-knowledge bug.

That's a bit light. Let me see.

Actually, let me approach this more conservatively. The article is already pretty clean. I'll just polish and add small touches of dry humor.

Let me try again:

Title: "Zcash vulnerability enabled 'unlimited' counterfeit minting; ZEC drops 31%"

A security researcher discovered a critical vulnerability in Zcash's Orchard transaction pool that could be exploited to mint an "unlimited" amount of counterfeit tokens within the pool. Shielded Labs, an independent Zcash support organization, published the findings on X on Thursday. It said it hired security engineer Taylor Hornby to conduct a review of the protocol in April.

The announcement coincided with a steep decline in the price of Zcash (ZEC). It fell 31% over the past 24 hours to $409.64 as of 11:00 p.m. ET on Thursday, according to The Block's ZEC price page. Much of the decline occurred in the five hours following the post's publication. The timing was, charitably, suboptimal.

Hornby, a long-time contributor to the Zcash ecosystem, evaluated the protocol using both AI-assisted and traditional security research techniques to identify vulnerabilities before they could be exploited by malicious actors, according to the post.

On May 29, Hornby discovered the Orchard circuit vulnerability using Anthropic's newly released Opus 4.8 model and immediately shared the findings with engineers at the Zcash Open Development Lab (ZODL). The Orchard pool is Zcash's shielded transaction pool, allowing users to send and receive ZEC with full zero-knowledge privacy. The Orchard circuit is a zero-knowledge proof system that ensures only valid transactions are accepted in the pool.

"The vulnerability was real and exploitable," Shielded Labs wrote. "Taylor, with the help of Opus 4.8, wrote a complete exploit which, when he tested it in a local regtest environment, generated unlimited, undetectable counterfeit ZEC."

The post explained that the vulnerability stemmed from an "under-constrained" element of the Orchard circuit, which made it possible to enter arbitrary false inputs to an elliptic curve multiplication and still have it approved. Privacy, ironically, made the flaw harder to spot.

Hmm, that's adding interpretation. Let me skip that.

The post explained that the vulnerability stemmed from an "under-constrained" element of the Orchard circuit, which made it possible to enter arbitrary false inputs to an elliptic curve multiplication and still have it approved.

While the vulnerability was patched on June 1, it has been present since Orchard's activation in May 2022, Shielded Labs said. A roughly three-year head start is generous, even for a stealth bug.

That adds humor. Let me think if it's too much.

Shielded Labs wrote in its post that the privacy properties of Orchard and the nature of the vulnerability make it difficult to know whether the pool had been exploited before discovering the flaw. Despite the uncertainty, Shielded Labs said the team is not "overly concerned" that counterfeiting took place before the bug was fixed, as the vulnerability has gone under the radar for many years, even under the scrutiny of the world's best cryptographers. Cryptographers, it seems, had other things to look at.

Hmm, that's a bit much.

Let me try: "The world's best cryptographers, apparently, were looking elsewhere."

That's a bit much too. Let me be more measured.

Let me look at the actual quotes and add very light touches:

"The discovery was not accidental — it was the result of a deliberate effort to identify vulnerabilities of this kind before malicious actors could," the post said. "[Hornby] used the most recent AI tools, available only to white-hat security researchers, along with a sophisticated custom-built AI harness and prompts, and worked hard to outrace the attackers. We think he probably succeeded."

While Shielded Labs said that actual exploitation of this vulnerability is unlikely, its team is exploring a proposed network upgrade to allow anyone to verify the integrity of the Zcash supply and prove that there are no counterfeit Zcash in the Orchard pool. The proposal would also deploy a new shielded pool and enforce turnstile accounting on all coins in the Orchard pool.

"This was a serious vulnerability, and we believe it's important to be transparent about what it means for Zcash users," the post said. "While no one wants to discover a vulnerability like this, we're confident that Zcash is well-positioned to recover." The market's vote of confidence, at least for one Thursday night, was less so.

Hmm.

Let me try to keep the humor very minimal and let the article breathe. I'll add maybe 2-3 light touches throughout.

Final approach:

Title: "Zcash vulnerability enabled 'unlimited' counterfeit minting; ZEC drops 31%"

A security researcher discovered a critical vulnerability in Zcash's Orchard transaction pool that could be exploited to create an "unlimited" amount of counterfeit tokens within the pool. Shielded Labs, an independent Zcash support organization, published the findings on X on Thursday. It said it hired security engineer Taylor Hornby to conduct a review of the protocol in April.

The announcement coincided with a steep decline in the price of Zcash (ZEC). It fell 31% over the past 24 hours to $409.64 as of 11:00 p.m. ET on Thursday, according to The Block's ZEC price page. Much of the decline occurred in the five hours following the post's publication. The market, briefly, disagreed with the recovery thesis.

Hornby, a long-time contributor to the Zcash ecosystem, evaluated the protocol using both AI-assisted and traditional security research techniques to identify vulnerabilities before they could be exploited by malicious actors, according to the post.

On May 29, Hornby discovered the Orchard circuit vulnerability using Anthropic's newly released Opus 4.8 model and immediately shared the findings with engineers at the Zcash Open Development Lab (ZODL). The Orchard pool is Zcash's shielded transaction pool, allowing users to send and receive ZEC with full zero-knowledge privacy. The Orchard circuit is a zero-knowledge proof system that ensures only valid transactions are accepted in the pool.

"The vulnerability was real and exploitable," Shielded Labs wrote. "Taylor, with the help of Opus 4.8, wrote a complete exploit which, when he tested it in a local regtest environment, generated unlimited, undetectable counterfeit ZEC."

The post explained that the vulnerability stemmed from an "under-constrained" element of the Orchard circuit, which made it possible to enter arbitrary false inputs to an elliptic curve multiplication and still have it approved.

While the vulnerability was patched on June 1, it has been present since Orchard's activation in May 2022, Shielded Labs said. Three years is a respectable run for a stealth bug in a zero-knowledge circuit.

Shielded Labs wrote in its post that the privacy properties of Orchard and the nature of the vulnerability make it difficult to know whether the pool had been exploited before discovering the flaw. Despite the uncertainty, Shielded Labs said the team is not "overly concerned" that counterfeiting took place before the bug was fixed, as the vulnerability has gone under the radar for many years, even under the scrutiny of the world's best cryptographers.

"The discovery was not accidental — it was the result of a deliberate effort to identify vulnerabilities of this kind before malicious actors could," the post said. "[Hornby] used the most recent AI tools, available only to white-hat security researchers, along with a sophisticated custom-built AI harness and prompts, and worked hard to outrace the attackers. We think he probably succeeded."

While Shielded Labs said that actual exploitation of this vulnerability is unlikely, its team is exploring a proposed network upgrade to allow anyone to verify the integrity of the Zcash supply and prove that there are no counterfeit Zcash in the Orchard pool. The proposal would also deploy a new shielded pool and enforce turnstile accounting on all coins in the Orchard pool.

"This was a serious vulnerability, and we believe it's important to be transparent about what it means for Zcash users," the post said. "While no one wants to discover a vulnerability like this, we're confident that Zcash is well-positioned to recover." The price chart, at least for one Thursday night, begged to differ.

Disclaimer: The Block is an independent media outlet that delivers news, research, and data. As of November 2023, Foresight Ventures is a majority investor of The Block. Foresight Ventures invests in other companies in the crypto space. Crypto exchange Bitget is an anchor LP for Foresight Ventures. The Block continues to operate independently to deliver objective, impactful, and timely information about the crypto industry. Here are our current financial disclosures. © 2026 The Block. All Rights Reserved. This

Hmm, "begged to differ" is decent. Let me review and polish more.

Actually, I think this is good. Let me check facts and numbers one more time:

• Critical vulnerability in Orchard transaction pool ✓
• "unlimited" amount of counterfeit tokens ✓
• Shielded Labs published on X on Thursday ✓
• Hired Taylor Hornby in April ✓
• ZEC fell 31% to $409.64 ✓
• 11:00 p.m. ET on Thursday ✓
• May 29 discovery ✓
• Opus 4.8 ✓
• ZODL ✓
• Vulnerability patched June 1 ✓
• Present since May 2022 activation ✓
• All quotes preserved ✓

Title check: "Zcash vulnerability enabled 'unlimited' counterfeit minting; ZEC drops 31%" - 9 words. Good.

Let me finalize and make sure I have exactly 12 paragraphs.

Wait, I had 12 paragraphs in original counting. Let me count my version:

1. Discovery paragraph
2. Price drop paragraph
3. Hornby methods
4. May 29 discovery
5. Quote
6. Under-constrained explanation
7. Patched June 1, present since May 2022
8. Actual